bring .vimrc up to date with multiple changes (nothing drastic)

* clean up some comments which were taken from some boilerplate config i
had started from years ago
* move some lines around to pretend there's a structure
* update the plugins list
* update key remaps: nnoremap <Space> : is more comfortable than
nnoremap ; : (though it was fine, too) + i'm trying out a way to move
around in normal mode and still have workman-p. the latter required to
move <C-o>, but it worked out alright.