Rename STYLEGUIDE.md to CONTRIBUTING.md, so GitHub would notice it.
documentation for test and function (closes: #734)

plus speling in documentation for bind.
Note that this commit does not re-enable the generation of the manpage for
test, which will therefore still fall through to the system manual page with
`man test`.
builtin_test: drop unused condstr
git_prompt: Informative upstream with informative status

This makes $__fish_git_prompt_showupstream = "auto" mean "informative"
instead of "git" if $__fish_git_prompt_show_informative_status is set.
git_prompt: Show upstream with informative status

This makes $__fish_git_prompt_show_informative_status imply
$__fish_git_prompt_showupstream = "informative", while adding a none
option for showupstream to disable it if desired.
git_prompt: Change informative character defaults

This changes the defaults for several characters when
$__fish_git_prompt_show_informative_status is set so that the prompt
looks more like the typical informative prompt.

Before:  (master >1<2|+3#4*5%6)
After:   (master↑1↓2|●3✖4✚5…6)

The defaults were taken from magicmonty/bash-git-prompt
git_prompt: Make informative separator configurable

It reuses $__fish_git_prompt_char_stateseparator, since it has a
similar meaning and goes otherwise unused when
$__fish_git_prompt_show_informative_status is set.
Fixes broken link in docs. Fixes #943
.gitignore: ignore generated source docs, don't ignore Doxyfile.help

Doxyfile.help isn't generated
git_prompt: Fix bad test if bash.showUntrackedFiles isn't set
git_prompt: Default upstream_prefix to nothing

git.git's __git_ps1 doesn't have an upstream prefix. I'm not sure why
one was added to our __fish_git_prompt, but it certainly shouldn't
default to a space.
docs: add editor documentation, move binding information

closes #931
also fixes a crossreference error
accidentally reopened #943, fixed now