Add base16_shell theme

base16_shell theme for vim-airline matches an active Base16 Shell
theme.

It should be used in combination with Base16 Shell, which sets the
correct colors in the terminal:
(https://github.com/chriskempson/base16-shell).

The colors used in this theme are within the 21 term colors set by
Base16 Shell.  The theme supports 2 options described in the docs.

autoload/airline/themes/base16_shell.vim

@@ -0,0 +1,99 @@
+let s:improved_contrast = get(g:, 'airline_base16_improved_contrast', 0)
+let s:solarized         = get(g:, 'airline_base16_solarized', 0)
+
+" Base16 term color palette
+let s:base00_black   = 0
+let s:base08_red     = 1
+let s:base0B_green   = 2
+let s:base0A_yellow  = 3
+let s:base0D_blue    = 4
+let s:base0E_magenta = 5
+let s:base0C_cyan    = 6
+let s:base05_white   = 7
+let s:base03_brblack = 8
+let s:base09         = 16
+let s:base0F         = 17
+let s:base01         = 18
+let s:base02         = 19
+let s:base04         = 20
+let s:base06         = 21
+
+" Gui color palette
+let s:gui_dark_gray       = '#202020'
+let s:gui_med_gray_lo     = '#3a3a3a'
+let s:gui_med_gray_hi     = '#303030'
+let s:gui_light_gray      = '#505050'
+let s:gui_lightlight_gray = '#8A8A8A'
+let s:gui_green           = '#99cc99'
+let s:gui_blue            = '#6a9fb5'
+let s:gui_purple          = '#aa759f'
+let s:gui_orange          = '#d28445'
+let s:gui_red             = '#ac4142'
+let s:gui_pink            = '#d7afd7'
+
+let g:airline#themes#base16_shell#palette = {}
+
+" Normal mode
+let s:N1 = [s:gui_dark_gray, s:gui_green, s:base00_black, s:base0B_green]
+let s:N2 = [s:gui_light_gray, s:gui_med_gray_lo, s:base04, s:base02]
+let s:N3 = [s:gui_green, s:gui_med_gray_hi, s:base0B_green, s:base01]
+
+if s:improved_contrast
+    let s:N2 = [s:gui_lightlight_gray, s:gui_med_gray_lo, s:base05_white, s:base02]
+endif
+
+if s:solarized
+    let s:N1 = [s:gui_dark_gray, s:gui_green, s:base01, s:base04]
+    let s:N2 = [s:gui_light_gray, s:gui_med_gray_lo, s:base00_black, s:base02]
+    let s:N3 = [s:gui_green, s:gui_med_gray_hi, s:base04, s:base01]
+endif
+
+let g:airline#themes#base16_shell#palette.normal = airline#themes#generate_color_map(s:N1, s:N2, s:N3)
+let g:airline#themes#base16_shell#palette.normal_modified = {
+            \ 'airline_c': [s:gui_orange, s:gui_med_gray_hi, s:base09, s:base01, ''],
+            \ }
+
+" Insert mode
+let s:I1 = [s:gui_med_gray_hi, s:gui_blue, s:base01, s:base0D_blue]
+let s:I3 = [s:gui_blue, s:gui_med_gray_hi, s:base0D_blue, s:base01]
+let g:airline#themes#base16_shell#palette.insert = airline#themes#generate_color_map(s:I1, s:N2, s:I3)
+
+if s:solarized
+    let s:I1 = [s:gui_med_gray_hi, s:gui_blue, s:base01, s:base0A_yellow]
+    let g:airline#themes#base16_shell#palette.insert = airline#themes#generate_color_map(s:I1, s:N2, s:N3)
+endif
+
+let g:airline#themes#base16_shell#palette.insert_modified = copy(g:airline#themes#base16_shell#palette.normal_modified)
+
+" Replace mode
+let s:R1 = [s:gui_dark_gray, s:gui_red, s:base01, s:base08_red]
+let s:R3 = [s:gui_red, s:gui_med_gray_hi, s:base08_red, s:base01]
+let g:airline#themes#base16_shell#palette.replace = airline#themes#generate_color_map(s:R1, s:N2, s:R3)
+
+if s:solarized
+    let s:R1 = [s:gui_dark_gray, s:gui_red, s:base01, s:base09]
+    let g:airline#themes#base16_shell#palette.replace = airline#themes#generate_color_map(s:R1, s:N2, s:N3)
+endif
+
+let g:airline#themes#base16_shell#palette.replace_modified = copy(g:airline#themes#base16_shell#palette.normal_modified)
+
+" Visual mode
+let s:V1 = [s:gui_dark_gray, s:gui_pink, s:base01, s:base0E_magenta]
+let s:V3 = [s:gui_pink, s:gui_med_gray_hi, s:base0E_magenta, s:base01]
+let g:airline#themes#base16_shell#palette.visual = airline#themes#generate_color_map(s:V1, s:N2, s:V3)
+
+if s:solarized
+  let s:V1 = [s:gui_dark_gray, s:gui_pink, s:base01, s:base0F]
+  let g:airline#themes#base16_shell#palette.visual = airline#themes#generate_color_map(s:V1, s:N2, s:N3)
+endif
+
+" Inactive window
+if s:improved_contrast
+    let s:IA = [s:gui_dark_gray, s:gui_med_gray_hi, s:base04, s:base01, '']
+else
+    let s:IA = [s:gui_dark_gray, s:gui_med_gray_hi, s:base03_brblack, s:base01, '']
+endif
+let g:airline#themes#base16_shell#palette.inactive = airline#themes#generate_color_map(s:IA, s:IA, s:IA)
+let g:airline#themes#base16_shell#palette.inactive_modified = {
+            \ 'airline_c': [s:gui_orange, '', s:base09, '', ''],
+            \ }

doc/airline-themes.txt

@@ -29,6 +29,7 @@ Currently this repository contains the following themes:
     * badcat
     * badwolf
     * base16(|airline-theme-base16|)
+    * base16_shell(|airline-theme-base16_shell|)
     * base16_3024
     * base16_apathy
     * base16_ashes
@@ -163,6 +164,29 @@ Uses a predefined colorpalette for defining the colors, instead of guessing
 the values from other highlight groups. To enable it: >
 
     let g:airline#themes#base16#constant = 1
+<
+                                                  *airline-theme-base16-shell*
+
+base16_shell theme for vim-airline matches your active Base16 Shell theme.
+
+It should be used in combination with Base16 Shell, which sets the correct
+colors in the terminal: (https://github.com/chriskempson/base16-shell). The
+colors used in this theme are within the 21 term colors set by Base16 Shell.
+The theme supports 2 options described below.
+
+*g:airline_base16_improved_contrast*
+
+Improves the contrast for the inactive statusline. To enable it: >
+
+    let g:airline_base16_improved_contrast = 1
+<
+
+*g:airline_base16_solarized*
+
+Adjusts the colors to match base16_solirazed shell theme. You may also try to
+use it with other Base16 Shell themes. To enable it: >
+
+    let g:airline_base16_solarized = 1
 <
 ==============================================================================
 CONTRIBUTIONS                                *airline-themes-contributions*