svn.8286: Added preliminary emulation of the famicom keyboard add-on (through a new driver fami_key, to avoid having to switch between full/partial keyboard emulation in nes & famicom).

Now the various BASIC carts start showing something:

known limitations:
- no tape support yet
- only the Famicom keyboard is emulated, so far: no support for Subor and other Study Cartridge & Edu Computer famiclones
- keyboard layout is not 100% accurate

EDIT: thanks to the keyboard matrix borrowed from FCEUMM, support for the Subor keyboard was very easy.

you can see that I correctly hit 15 keys over 18, so the new inputs are fine (the remaining 3 were missed because I was slow in pressing the buttons wink ).
the "preliminary" comment in both commits refers to the not perfect mapping and to the fact I still have to research about which IO ports should be in use and which should be disabled when keyboards are read... but games should simply work fine!

I think FC + Subor keyboards cover most available carts; remaining Edu carts requiring different keyboard controllers should probably be emulated as separate drivers (only sharing with NES the core emulation)