UPDATE: remove unnecessary padding.

FIX: stim_channel, filtering

FIX: stim_channel as str, ch dict for misc, UPDATE: _read_segment

Added warning if the sampling frequency is different among the
channels. Now handles data where channels have different sampling
frequencies.

WIP resample

FIX resampling implemented for differently sampled data.

COSMITS

COSMITS: nchan -> n_chan

ADD: test for unequal sampling

UPDATE: remove unnecessary padding.

RM: test_unequal