Changes in version 0.3.1

Other changes:

Fix initialization when sourcing zsh-syntax-highlighting.zsh via a symlink
(083c47b007)

Run each test in a separate subprocess, isolating them from each other
(d99aa58aaa, et seq)
Fix test failure with nonexisting $HOME
(#216, b2ac98b981)

suffix aliases (requires zsh 5.1.1 or newer):
```
  alias -s png=display
  foo.png
```
prefix redirections:
```
  <foo.txt cat
```
redirection operators:
```
  echo > foo.txt
```
arithmetic evaluations:
```
  (( 42 ))
```
$'' strings, including \x/\octal/\u/\U escapes
```
  : $'foo\u0040bar'
```
multiline strings:
```
  % echo "line 1
  line 2"
```
string literals that haven't been finished:
```
  % echo "Hello, world
```
command words that involve tilde expansion:
```
  % ~/bin/foo
```

quoted command words:
```
  % \ls
```
backslash escapes in "" strings:
```
  % echo "\x41"
```
noglob after command separator:
```
  % :; noglob echo *
```
glob after command separator, when the first command starts with 'noglob':
```
  % noglob true; echo *
```
the region (vi visual mode / set-mark-command) (issue #165)
redirection and command separators that would be highlighted as path_approx
```
  % echo foo;‸
  % echo <‸
```
(where ‸ represents the cursor location)
escaped globbing (outside quotes)
```
  % echo \*
```

(Start of changelog.)