Agkozak Zsh Prompt Versions Save

When the local git version is 2.15.0 or greater, git status will not run unnecessary optional operations that require locks.

• The subst-async method now works correctly on ZSH v5.0.2, but
• The usr1 method will be the default on ZSH v5.0.2, as it should be slightly faster than subst-async

By default, a space precedes the Git branch status indicator. The space can now be eliminated by setting AGKOZAK_BRANCH_STATUS_SEPARATOR='', or changed to another character or characters (e.g. AGKOZAK_BRANCH_STATUS_SEPARATOR='--').

• The array AGKOZAK_PROMPT_CHAR allows the user to specify prompt characters for regular user, superuser, and vi command mode.
• Setting AGKOZAK_COLORS_PROMPT_CHAR can change the color of the prompt character.
• The array AGKOZAK_CUSTOM_SYMBOLS contains user-specified symbols for displaying the Git status.

• Removes use of external command cat in usr1 async method
• Uses latest commit of zsh-async that avoids infinite loops due to corrupted file descriptors

I have restored the _agkozak_vi_mode_indicator function as a legacy feature, as many people people use it in custom prompts. The default indicator can be expressed as '%(4V.:.%#)', though, and variations on this will be preferable to '$(_agkozak_vi_mode_indicator)', which entails a subshell.

New in this release:

• The asynchronous Git status is now available via process substitution in all supported versions of ZSH and on all supported systems (props to @psprint). For reasons of speed, zsh-async remains the default asynchronous method in WSL and Solaris, and usr1 is default in MSYS2/Cygwin.
• AGKOZAK_LEFT_PROMPT_ONLY - when set to 1, the Git status is displayed in the left prompt, and the right prompt is blank.

Improvements:

• The prompt script loads up to 4x faster.
• The left prompt displays ~2x faster.

• The prompt uses termcap sequences only with FreeBSD and DragonFly BSD; terminfo with other BSDs
• No ugly escape sequences on DragonFly BSD's cons25 console
• If $HOME happens to be / (as is the case for root on Solaris 10), the path will be displayed correctly when AGKOZAK_NAMED_DIRS=0
• One subshell eliminated when remote/local status is being calculated

By making intelligent assumptions about TERM and OSTYPE, the prompt can frequently avoid running two external commands in subshells as it starts up. The difference is noticeable on Windows (MSY2/Cygwin/WSL).