onesecepoch cleanup

[mmagnuski]

• name is a bad description of what the function does; segment_continuous or just segment_eeg would be better. Current segment_eeg segments epochs so should be renamed or thrown away (this is almost never used...)
• add english docs
• rewrite window selection to:
  • loop through relevant events, not windows (would be easier to read)
  • accept distances like [2, 4] (not closer than 2 secs, but not further than 4 secs) or [-4, -2] etc.
  • vectorize a little more
• anything (including window selection) that would be useful outside onesecepoch should be taken out and made a separate function