This adds MCO source selection to some targets, and removes and standardizes
the mask/shift usage for all targets. For devices that support MCO2, this
supports only MCO1. No attempt has been made to extract MCO prescaler, which
is not available on all F1 and F3.
So that the navigation pane works correctly in browsers.
Some additional doc fixes put in where found (but many more still to go).
Added some dummy .c and .h files to bring the associated docs into line.
makefile changed to allow 'make html' as well as 'make doc' (the latter only does html anyway).
