[vim] Add :nunmap and a simple test

In Vim, defaults keymap cannot be unmapped. They must be explicityly
set to <NOP>. In this case we allow that because
user defined maps are stored in the same map as the defaults.
[clike mode] Support C++11 unicode & raw strings
Fix linting (missing semicolon)
[pig-hint addon] Remove

It was broken and confused.

Make the mode register a list of completable words instead.

Issue #2324
[vim] Implement visual_o
Merge branch 'master' of https://github.com/marijnh/CodeMirror into registers
added support for :reg[isters] command