Update Oh My Fish.

== USAGE
  omf update [<package1> [<package2> [...]]]

== DESCRIPTION
Update Oh My Fish, all package repositories, and all installed packages.

* When called without arguments, updates the core framework and all installed packages.
* You can choose to update only the core, by running `omf update omf`.
* For selective package update, list only the names of packages you wish to update. You may still include "omf" in the list to update the core as well.

== ALIASES
*omf u*, *omf up*