Adding new :command

Adding a command

1. Add it to src/cmd_handlers.c
2. Think about command id (in cmd_completion.h), its completion and whether this command should be whole-line kind of command.
3. Add it to data/man/vifm.1 (don't forget to update modification date).
4. Add it to data/vim/doc/app/vifm-app.txt (don't forget to update modification date).
5. Regenerate tags.c by running make.
6. add to tests/test-data/syntax-highlight/syntax.vifm.
7. add it to data/vim/syntax/vifm.vim (don't forget to update modification date).
8. Running scripts/check-syntax-changes should show changes in highlighting for new lines.
9. Remove from the TODO file.
10. Add to the ChangeLog file.
11. Add unit tests.

Map-command notes

1. Consider the following variants :X[un|nore]map.
2. Think whether :[un|nore]map or :[un|nore]map! commands should affect :Xmap.