Fixes zsh-users/zsh-syntax-highlighting#182.
Prerequisite for testing issue #228.

* tests/test-highlighting.zsh
  (run_test): Move functionality to run_test_internal; make run_test be a wrapper
    that handles creating and cleaning up the tempdir.

* tests/README.md: Document the new feature.

* "highlighters/main/test-data/path-space- .zsh"
* highlighters/main/test-data/path-tilde-named.zsh
* highlighters/main/test-data/path.zsh
    Change test data to not depend on being run from the source directory.

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

Signed-off-by: Takeshi Banse <takebi@laafc.net>

* 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>