API/WIP: new io module

Just to let you know I'm on it ;-) This addresses our discussion in #383 and the discussion we had while adding BTi and KIT support.
This is still WIP but the fiff module now is deprecated, and you can import mne + the new name space.
Before going on and changing the tests and the examples It would make sense to make sure we converge on the proposed change.

Let me briefly summarize how I  wrapped up our discussion so far.
- fiff will be moved to io where it is at the same level as bti and kit, so mne.io.fiff, mne.io.bti, mne.io.kit
- functions related to reading raw files will be available in mne.io, compliant with an read_XXX API
- I hope you're with me with regard to these two last points. 
- some important functions, e.g., pick_types, read_evoked,  will be linked to the mne name space. Here I would like to poll which functions we would like to see in the mne name space.