In region_highlight, a spec of the form 'i j foo' with i >= j should have no effect.
Before this commit, however, the {$i..$j} range would happily expand to (5 4 3)
if i > j were the case (e.g., i=5 and j=3).
This breaks vanilla-newline.zsh; the next commit will fix that.
* Don't override user defined styles
* Better modularisation of highlighters
* Allow to define which highlighters are activated
* Allow to define the order in which they are defined
* Minor performance optimizations
* Fixed some variables leak
* Improve documentation
* Brackets highlighter: use ZSH_HIGHLIGHT_STYLES instead of a specific array
