Move tests on the highlight path until after the blacklist is checked so
that blacklisted paths are not tested. This should prevent hangs on dead
remote filesystems provided the path is blacklisted in
X_ZSH_HIGHLIGHT_DIRS_BLACKLIST.

Updated tests to 'default' highlight as the blacklist is now checked
before the path is tested.

Bug: https://github.com/zsh-users/zsh-syntax-highlighting/issues/528

Closes #379.

Closes #468.

The fix for issue #9 was accidentally broken by the penultimate commit.

Note that we don't care about aliases to ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR
entries, since the code deals with aliases at command position.

All these files should be sourced, not executed; and Debian's lintian complains:

W: zsh-syntax-highlighting: script-not-executable usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh

Fixes zsh-users/zsh-syntax-highlighting#189.

Fixes zsh-users/zsh-syntax-highlighting#181.

* 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

Feel free to add more test data !

Signed-off-by: Julien Nicoulaud <julien.nicoulaud@gmail.com>