Removed armasm from gitmodules.
Removed vim-slim plugin.
Removed vim-commentary plugin; haven't used it.
Removed ack.vim plugin; seldom used. Maybe add it back later.
Removed non-submodule arduino plugin/syntax.
Added sudar/vim-arduino-syntax as submodule.
Removed bufexplorer plugin; barely used.
Removed (already-commented-out) Ack config from vimrc.
Removed asmsyntax = "armasm" from vimrc.
Don't auto-reload .vimrc on edit; bad things always happen.

(Powerline / Airline (status-bar at bottom) always seem to break
when .vimrc is re-sourced at runtime.)
Remove FocusLost auto-save handler; that was GUI-only.
Additional comment explaining `set mouse=a`.
Tidied vimrc; particularly Keyboard and Shortcuts section.
Updated airline; 31 commits.
Updated checksyntax; 6 commits.
Updated coffeescript; 6 commits.
Updated ctrlp; 17 commits.
Updated eunuch; 16 commits.
Updated fugitive; 68 commits.
Updated golang; 14 commits.