Improve smart-tab insertion/deletion; fold toggle.

Add:
	vimrc
		-add BlockSmartTab() and BlockSmartBackspace(), which allow the
		SmartTab() and SmartBackspace() functions to operate on visual
		selections at a time.
		-add ToggleUniversalFold(), to allow toggling of all folds
		simultaneously in the current buffer.

Mod:
	vimrc
		-improve BlockSmartBackspace(), which now deletes to the start of the
		current indent independent of whether or not its at the end of that
		indent (ie, doesn't have to be &tabstop ahead of the last location
		evenly divisible by &tabstop).