miscellaneous typos
status command: improve help text
index.hdr.in: add code markup
index.hdr.in: (hopefully) non-controversial edits
index.hdr.in: slightly more controversial changes

 - Clarify wording in functions section
 - Use the term aliases rather than wrappers
 - Clarification of concepts and better? examples in variable expansion
 - Likewise in environment variables
 - Using the phrase builtin commands rather than builtins
 - Tidy up keybindings a bit
 - Another example in the history section
 - Remove TODO section in favour of mailing list, GitHub and IRC link
Add a note about getting help through man pages
Merge branch 'zanchey-docs'

Conflicts:
	doc_src/index.hdr.in
Clarify "input/output methods" in documentation
Manually cleaned up Mercurial completions.
Add completions for cabal; closes #567
Added documentation for printf

Fix for https://github.com/fish-shell/fish-shell/issues/488
Avoid generating man page and help section for printf (to fallback on system man page for printf)
Formatting and style updates
Typos in the fish OS X package installer rtf file
Correct sizes of certain fish.app icons
Doc fix where wrong file was referenced in an example
Attempt again to fix UnicodeDecodeError (issue #658)
Prevent fish dying if setupterm() fails in builtin_set_color()

Since set_color was changed to a built-in command, the entire shell will
exit in the event that setupterm() fails for some reason since ncurses
does an exit() if an errret was not passed in.

setupterm() can fail if the TERM environment variable is not set. This can
cause the shell to die prematurely if set_color is called from a startup
file like config.fish (such as vi-mode.fish which caches the results of
set_color when it is loaded) and fish is started without a TERM set
(e.g. when started from .xsession, or when being used as a remote shell
by a command such as rsync, scp or git)

A simple repro case for this issue is:

ian@delenn~ [i]> echo set_color normal > ~/.config/fish/config.fish
ian@delenn~ [i]> scp localhost:test .
TERM environment variable not set.
ian@delenn~ [i]>

This patch passes in an errret variable to setupterm(), which causes
ncurses to return the error to builtin_set_color() rather than calling
exit():

ian@delenn~ [i]> scp localhost:test .
test                                                 100%    0     0.0KB/s   00:00
ian@delenn~ [i]>

Signed-off-by: Ian Munsie <darkstarsword@gmail.com>
Add errret param to other calls to setupterm
documentation typos