vimrc: distinguish zsh path on Linux
vimrc: remove supertab plugin
vimrc: fix python auto-indent on new line
vimrc: add vim-sneak plugin
vimrc: disable ultisnips plugin for now

Also: move Riv configuration into alpha sort order within plugin config
blocks
vimrc: configure Ctrl-P plugin to ignore .tox dir
vimrc: disable Syntastic in RestructuredText files
vimrc: break line at column 77 in Python files
vimrc: silence error on FocusLost on unnamed file
vimrc: don't open preview window on function match
vimrc: turn off '-- More --' msg on long output
vimrc: reduce second-keystroke timeout to 1 second
vimrc: add <leader>h toggle search highlight
vimrc: fix ToggleRelativeNumber in new Vim version
vimrc: add Emacs movement keys in insert mode
vimrc: stage unmaps for vim-commentary
alias: correct a couple aliases