Added rectify_chanels
renamed cnt_to_epo to segment_cnt
Don't remove void classes in select_epochs or remove_epochs.

* fixed all unittests and also check if the void classes are not removed
* fixed docstrings.
Fixed many single backticks to double backticks.
Renamed segment_cnt to test_segment_cnt
Changed subsample signature from cnt, factor -> cnt to cnt, freq -> cnt

Docstrings, unittests and examples.
Added new Data class which is the base for all Cnt, Epo and FV data.
Added swapaxes + tests.
Updated select/remove_channels to use new Data

updated tests as well.
Updated select/remove_epochs to use new Data

updated tests as well
Updated subsample to use new Data.

updated test as well.
Updated calculate_classwise_average for new Data

updated tests as well.
Updated correct_for_baseline for new Data

updated tests as well.
Updated rectify_channels to use new Data

updated tests as well.
Updated select_ival to use Data.

Updated tests as well.
Added test in constructor of Data to check if the axes have the same lengths as
the axes in data.

Fixed unittests.
Updated jumping_means for new Data

added tests for jumping_means
updated segment_cnt to use Data

- renamed to segment_dat
- updated tests
- don't modify marker anymore
Added various *axis parameter descriptions in docstrings.
Fixed docstring for unittest.