Add utility function _lp_bool

_lp_bool converts a return code (default to $?) into a "true"/"false"
value.
Fix #304: _lp_jobcount_color() when is tmux not installed

Refactor _lp_jobcount_color() to avoid running either 'screen' or 'tmux'
if they are not installed.
More _lp_jobcount_color refactoring
Simplify chroot detection code
Synchronize rc, theme, and ps1 files with main file
Fix LP_OLD_PROMPT_COMMAND to work with zsh
Fix *BSD support for terminal colours
Simplifiy git working tree detection

Thanks to @pkkolos (Panayiotis Kkolos <pkkolos@gmail.com>) for the inspiration.
https://github.com/pkkolos/liquidprompt/commit/63e1b8229ba122de3db4c747704d5a13a4b4a109
Count merge commits in git when checking differences with tracking remote branch
Fix mark prefix

Now the prompt mark can be at the beginning
of a new line without a space before it.

Conflicts:
	liquidprompt
Simplify LP_MARK_DEFAULT definition

Thanks for inpiration to @pkkolos.
Fix typos in code comments

Thanks to @pkkolos for catching them in
https://github.com/pkkolos/liquidprompt/commit/1eb35f46b0918974cebe351ca8441e4659b869a5
Fix _lp_bzr_branch_color for zsh

Fixes #301 without affecting bash functionality
Subversion: fix branch/tag extraction

That was broken for a long long long... time.
Should close #117, #237 and is an alternative to patch proposed by
@anthonygelibert in #264.
README: use a true (Unicode) em dash
README: minor fixes
Add the text of the LICENSE (AGPL 3)

... and link to it from README
test.sh: fix fake acpi for -t
bash: save and set shell option promptvars
Remove variable LP_LIQUIDPROMPT, redundant with LP_OLD_PS1