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This PR fixes the runtime error that displays this:

```log
prompt_status:2: symbols: attempt to assign array value to non-array
```.

It trips over a local array which is not properly declared.

* agnoster: do not hardcode black foreground.

This would allow easy customization when using light color schemes, like
solarized-light

* agnoster: implement light theme variant

Use same variable as in blinks theme, to detect if solarized theme used
is a light or dark one.

* use https everywhere

* use https links on the files that are left

Also, removed some broken links and updated redirections.

The PROMPT building method clashes with other themes and
plugins that modify the PROMPT variable.

Also reverted the $jobstates trick due to it not working
inside $PROMPT.

* agnoster: improve perf with use of $jobstates (zsh/parameter module)

This saves multiple fork/execs (for the subshell and wc) each
time the prompt is rendered

* agnoster: compute git repo_path only when in a git repo

this avoids needlessly invoking git twice every time we render the prompt

* agnoster: avoid subshell when rendering prompt

Rather than forking a subshell to print the prompt, construct it
incrementally by appending to $PROMPT.

v2: fix incorrect CURRENT_BG
v3: fix bzr and hg prompting

Thanks @mcornella for the help.

Plugin command-not-found on Arch Linux returns 0 if git or bzr is found in repos, hence outputting unwanted pkgfile output.
Checking if the commands exist first fixes all such issues.

the agnoster theme is now able to render basic information
if the user is currently residing inside a bazaar folder.
if so, it will render a green promt segment with "bzr" and
the current revision number in it. if there are untracked
files, the bar will be rendered in yellow. if there are
changes to already tracked files, a + character will be
printed.

I noticed that for certain projects with unstaged changed I would get a 'U' character instead of the '●' character. This should fix that.

Problem

On detached-refs, the git prompt is very slow because it uses a command
to output all refs, which takes 32s on the twitter internal git repo.

Solution

Use git-rev-parse instead of git-show-ref to only output the head ref.
Runtime drops to 0.03 seconds.

Note

Interestingly, git-rev-parse isn't slow without the --head arguement so
I'll probably be cooking up a patch for the git team to speed this up
eventually, but it's still pointless to sigpipe git as it walks the
filesystem.

all platforms. Add clarifying comments. This makes everything consistent
with the current Powerline-patched fonts definitions.

This avoid spawning additional processes, as the $USER variable will
**always** contain the current logged-in user.

<B> Designates Bisecting
>M< Designates Merging
>R> Designates Rebasing

re-implemented expired pull request https://github.com/robbyrussell/oh-my-zsh/pull/1759

changed ± to 

clearing up some confusion in issue#1906

agnoster theme was checking if the default virtualenv prompt was turned off and not showing its own... so there was no way to see which virtualenv was selected.

See http://www.virtualenv.org/en/latest/index.html\?highlight\=virtual_env_disable_prompt\#activate-script for info regarding this.

This reverts commit baffc3b0.

The code points have been updated in 53fbfe1, see
- https://github.com/Lokaltog/powerline/commit/53fbfe15fead8cc7598bcb4ee9714a221ab7e446
- https://github.com/Lokaltog/powerline/issues/4

IMPROVED: untracked file status has priority over modified (ie: if you have both modified and untracked files, your prompt will be red indicating the presence of untracked files)

This reverts commit f09af571.

It is far more aesthetically pleasing, and conveys the correct amount of information. The exact numeric status code is extremely rarely of use, and increases cognitive parsing burden on the user.
(cherry picked from commit 8f664edcaf55adcc540f0fe43d4205b66e4f9fb6)