Added owner frame to option dialogs.
Search text: don't search if search string is empty.
Removed custom zipper implementation since the difference in performance is small.
Removed unsued function in lab.util. Moved find-char as a util function.
Search text: add results of the search as items in the dialog list showing the line where the match was found.
Fixed bugs: file explorer close button handler was not being declared, next and prev tab commands threw errors when there were no editor tabs.
Reorganized some test files.
Fixed typo and remove ellipsis from command name.
Created tests for keymaps. Added function to remove a keymap in a hierarchy of keymaps and a multimethod to unregister keymaps.
Added a bug to BUGS and reformatted lab.core.md.
Added assertions to keymap tests.
Plugin: Implemented the core functionality for unloading a plugin. Added test for loading and unloading a plugin.