_lp_temp_sensors : a better use of sed

closes #189
_lp_color_map is now able to adjust to different scales

Given a second parameters, _lp_color_map is now able to display
different colors depending on a scale. The second parameter is the
lowest step on the scale and ten times it the highest.
the _lp_color_map will use a scale system

and not a step one
Simplify color map lookup

Thanks to François Schmidts (jaesisvm) for the previous work.
[enh] Add support for antigen autoloading
_lp_temperature: fix variable leak
Rename variable _lp_temp_function to _LP_TEMP_FUNCTION for consistency
smart mark: lowercase variable for code style consistency
Optimize as $EUID can't change during the shell life

$EUID will not change during the shell life. So we can optimize color
selection at liquidprompt startup instead of testing multiple times
every time the prompt is shown.
Optimizes LP_MARK and LP_PWD.
Move common code to 2 branches of an 'if' out of it

Still optimizing EUID...
Root: huge optimisation (and security feature) for VCS directories

If under root user, for VCS directories we do not collect anymore the
VCS status information. Before it was collected (even if
LP_ENABLE_VCS_ROOT=0, which is the default) but just not displayed.
This is a huge optimisation for VCS directories, and also a security
feature, as our shell code is absolutely not resistant to specially
crafted VCS content.
Add LP_DEBUG_TIME for bash: if 1 shows PS1 build time

Doesn't work on zsh: looks like 'time' doesn't output anything if
applied to a shell function. Need a zsh expert.
Color map: zsh fixes
Inline LP_PROXY building
Cleanup _lp_connection once done with it
Optimize _lp_smart_mark

Remove one _LP_SHELL_zsh test from runtime.
Introduce _LP_MARK_SYMBOL.
Optimize _lp_smart_mark more: case .. esac

Use a 'case..esac' in _lp_smart_mark.
Fix mark for root

I broke it in cf2ff289c8755019bba5dff271ae3d03a784fc5e.
Thanks to François Schmidts who immediately noticed the bug and produced
a patch (but that I choose to not apply).
Closes #201.
README: fix typo (closes #202)