[TREELIST] Fix dereferencing NULL pointer when deleting top-level item.
[TREELIST] Fixed crash in treelist_delete_notify()...

... when deleting all items using the magical MC_TLI_ROOT.
[misc] Fix typo in #error message.
[TREELIST] Add assert into treelist_scrolled_item().
[gdix] Improve comment.
[CHART] Fix using non-default axes exponent.
[THEME] Fix handle leak in mcGetThemeSysColorBrush().
[Makefile.dep] Commit outdated change.
Bump version to 0.9.4
[debug] Take advantage of __builtin_unreachable...

... for gcc under release build for implementation of MC_ASSERT.
It can provide a useful hints to the compiler for better optimization.

This also allowed sumpligying of definition for MC_UNREACHABLE.