lots of rewriting
code works correctly for calculating significance

rationale for F-stat may be wrong, however
still working on refactored significance procedure
integration tests for significance now passing

normalization of time-freq now happens outside _peri_event
default function for statistic comparison is the t statistic of
dB-converted power
added notebook exploring estimators for power ratio between conditions
clarification on relation to t stats
trying to implement new statistic
new statistic now working
added comparison with t-based approach
added option to have _peri_event remove chunks containing nan