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).
- Makefiles now include building f3 src directory.
- Gpio support added. gpio_common_f24 changed to support also f3.
- f3 still not compiling, but f2 compile not broken (probably also f4).
