ENH: Dump pandas

This is moving toward getting rid of pandas. I've stripped out all Pandas support. Tests pass over here, with only minor modifications (mostly to remove tests that made use of private parameters). This will cause some API changes, but hopefully this is okay since the user base is fairly small :)

There should be more red than green, which I think bodes well for future simplicity as well.

Remaining issues:

1. ~~Speed. I still need to optimize the code.~~

2. ~~Dealing with `find_custom_events`. Right now it won't work with EDF correctly, since the converted file is deleted immediately. It's not good to require the filename to be stored using something like `raw.info['fname']`, it is just asking for bugs. Can we either do without `find_custom_events` (the only thing that uses `info['fname']`, or at least make it so you must pass in the `fname` again to `find_custom_events`?~~

3. ~~`raw` having `time` as one of it's data fields (e.g., in `raw.info['data_cols']`. I will remove it. It's redundant with using `raw[:, :]` interface, which returns a `times, data` tuple. It's really more of an indexer than a type of data, so I still need to remove it.~~

4. Dataframe support. @dengemann hopefully you can add this one back in once this is settled?