Replace verbose insert-keymaps with abbrevs.

Add:
	vimrc
		-replace verbose, insert-mode keymaps intended to expand a sequence of
		letters to a full word or statement with abbreviations.
		-add EatSpace() function, to eat the additional whitespace inserted to
		trigger an abbreviation expansion.
		-convert all non-printable escape-keys (eg "<esc>", "<cr>") to
		lower-case.
Migrate ft autocommands to ftplugin/ files.

Ref:
	vimrc, vim/ftplugin/*.vim
		-move filetype-specific autocommands from vimrc to statements in
		filetype-specific files in vim/ftplugin, for greater modularity and to
		ease congestion in my vimrc.

	vimrc
		-replace numerous, parallel autocommand-groups with a single augroup for
		all autocommands; they were unnecessary, and instead of increasing
		readability with descriptive augroup names, decreased it by visually
		bloating the vimrc.