AH (Ad Hoc) waveform format read support

AH v1 should be fine.
AH v2 tests need some real examples + ASCII equivalents to finish this PR - unfortunatly I couldn't find anything useable :/

Anyone got some AH v2 files? @jsaul, @jwassermann?
In Python 3 bytestrings are valid for the format and the buffer arguments. The format can alternatively also be a string. Python 2 for some reason also accepts unicode strings as a buffer...In any case, the future module replaces `open()` with `io.open()` and the `"rb"` specifier therefore actually works and we should be fine in all cases.