Log g:easy_align_last_command
Implement live interactive mode (#15)

This commit adds LiveEasyAlign command. (The name was chosen not to introduce
ambiguity when typing in only the prefix of the command: e.g. `:EasyA*|`)
In live interactive mode, the selected text is aligned on-the-fly as the user
type in. In order to finalize the alignment, the user has to type in the
same delimiter key again. (Or CTRL-X on regular expressions)
Do not attach margin_left string before phantom token