Rebuild "ycm" compatible <BS> as a function. Add a new branch -_-!

About ues `DELETE` to trigger a ycm omni popup menu, i tred to overwite `DEL` as same way as `C-y` `BS` or `C-e` `BS` , but it's not work. -_-!!!

Maybe that ycm complete trigger not included `DEL`? Perhaps somebody can edit the source files to get that.