Parse packets based on channel caps instead of channel number

[cboulay]

Fixes #103
Fixes #104

• As much as possible, parse packets based on the channel capabilities instead of the channel number.
• Fixes a bug where digital in and serial in events were not being interpreted
• Fixes a bug where digital and serial data couldn't be above 6
• Fixes a bug where events (spikes, digital, and serial) were skipped if they came in packets between the calls to InitTrialData and GetTrialData. Note that user memory allocation occurs between these calls so this is a non-trivial amount of time.
• Updates Python wrapper with above changes.
• Python wrapper also updated to not reset the clock by default, even if the buffer is reset. I only did this where event data were involved. It might be true for continuous data too but I won't be able to test continuous data for a while.

[cboulay]

After this gets merged I'll tag a release and add some binaries. Until then, here's the py3.6 win64 wheel.

cerebus-0.0.3-cp36-cp36m-win_amd64.zip

[dashesy]

Thanks! there are just some minor formatting

[cboulay]

All modifications made except for the lack of constant for 128. I'd rather not define a constant for a single-use, especially if there's a reasonable plan to get rid of it in the not too distant future.