Make simple quickfix toggle plugin

Instead of mapping to cwindow (which only opens if there are
_recognized_ errors), use a function to make both switching to qf and
closing it easier.

Will open and switch to qf. If in qf, will close it.
Does the same for locationlist (but I don't use ll much).

Remove equivalent mappings from vimrc
Map q to quit the quick fix window

Only when opened with togglequickfix, but it will close the correct
window.
Only map q in the quickfix buffer

Only map q after we open (and jump to) a quickfix.
Make togglequickfix maps more consistent

Use <Leader>w as a prefix for toggling windows. Also do the same for
preview window (although there's no open).

I use <C-w>w a lot, so add a <Leader>w map for that.
Change quickfix map to wc

wq is much easier to type than wc and is a good mnemonic. I use this map
a lot, so I need it easy to type.
Rename togglequickfix to fixquick

Creating a general quickfix plugin for common conveniences.
Create some quickfix ftplugin maps

Move quit map to ftplugin where it will always work (no matter how
quickfix is opened).

Add some more useful maps for changing through quickfix history.
Summarize maps in readme