Implement delete rule
Refactoring
Update default rule
Fix test
Fix the cursor position when escape insertmode
Fix: special keys do not work in cmdline mode
Fix default rule: leave with single quote does not work
lexima is disabled when buftype=nofile
Do not use setcmdpos

When <CR> is mapped in cmdline mode, '=setcmdpos()' is remained
in commandline.
Implement leave rule on cmdline mode
Implement delete rule on command line
Can define altanative key (e.g. <C-h> as <BS>)
Add doc