Document how stupid append is.
Fixed append for negative axis values.
Fixed bug in segment_dat which would sometimes not recognise segments if the
respective markers are very close to the next element in `timeaxis`.

Updated tests and added more comments to explain the tests.
Revert "Added online subsampling capabilities."

This reverts commit b1a581d917c638d563cb7e1a792716fc0f86d1d6.
Updated docs for processing to give examples for online settings.
Fixed append_cnt to deal with timeaxis and markers correctly.

Updated tests and docstrings.
Added BlockBuffer

+ unittest
+ docs