Refactor color definition ; Cleanup colors once config is loaded

Now use TermInfo feature detection instead of just distinguishing if
"$OS == FreeBSD". This will allow support for more terminal definitions.

Cleanup color variables (BLACK, WHITE, BLUE, BOLD...) once the config
file has been loaded as color variables are not used at runtime.
Refactor config loading: step 1
Refactor config loading: step 2

Default settings are now set inside the _lp_source_config function
Refactor config loading: step 3 (indent)

Indent (separate commit just for readability of the step).
Refactor config loading: step 4

Move colors definitions inside _lp_source_config.
(The important part of the diff is that the beginning of the
_lp_source_config function is moving up).
Refactor config loading: step 5 (indent)

Just indenting lines in _lp_source_config after the move.
Refactor config loading: step 6

Move the 'local' keyword in front of where each color variable
is defined, for safer maintenance.
More comments
Cleanup _lp_source_config: remove _lp_ prefix from locals

Now that color definition utilities (_lp_ti_*) variables and functions
are "local" we do not fear to override someting defined by the user.
So just rename to shorter and cleaner names without the _lp_ prefix.
Unset _lp_source_config once done
More comments
Merge branch 'refactor/terminfo-sh' of https://github.com/dolmen/liquidprompt into develop
manual merge
Add support of /etc/debian_chroot

Debian uses the file /etc/debian_chroot to give a name to a chroot.
The default /etc/bash.bashrc contains:

if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)
fi

PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
Merge branch 'develop'
bugfix: consider every X screen as a local connection, not only the first one
Merge remote branch 'upstream/master'
Remove extra new line in case of SVN directory

Without the patch my prompt is (on 3 lines):
[rousseau:~/Documents/sc/nfc/libnfc]

svn ‡

With the patch my prompt is (on 1 line only):
[rousseau:~/Documents/sc/nfc/libnfc] svn ‡

This is because expr(1) adds a new line at the end of the result.
manual merge
Merge branch 'master' of https://github.com/LudovicRousseau/liquidprompt into develop