Fixes #694.

Fixes the bug the previous commit added a test for.

Suggested-by: @QBobWatson
(in https://github.com/zsh-users/zsh-syntax-highlighting/pull/682#issuecomment-588361771)

Fixes #656.
Fixes #660.

Regression from commit e1ecf950e23471b235e318ba7b85e77395a6b146,
"main: Do path expanstion after alias expansion" (sic).

Suggested by Daniel.

The test point is XPASSing, which makes CI red.  As a duct tape measure to turn
CI green again, update the test expectations to make it XFAIL.  The hacky part
is that the expectation set by this commit will never be met; the test point
will never XPASS now until its expectations are changed again.

Issue #623 remains open to track setting the test expectation to the correct
value (i.e., make the test XFAIL in a manner that _will_ XPASS if the bug is
fixed; in other words, pay off the technical debt created by this commit).

Issue #616 remains open to fix the actual bug.

Fixes #596

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>