Asammdf

Changes
- continuous integration with Travis CI (thank to Mihai)
- initial test (thank to Mihai)
- avoid unnecessary duplication of channels when filtering measurements with channel compositions

Fixes
- fixes for channel composition in mdf version 4 (thanks to Julien Grawe)
- multiple documentation fixes (thanks to Mihai)
- multiple fixes for mdf version 2 files

Changes
- support MDF version 2.14
- add new _resample_ method to _MDF_
- try to avoid _MemoryError_ for _append_ on 32 bit Python
- add _get_channel_comment_ and _get_channel_unit_ methods
- add save overwrite as configurable option
- added possibility to return pandas DataFrame to select method
- pandas is now a required dependency


Fixes
- use data block size equal to multiple of record size when splitting data blocks in mdf version 4 save
- fix default values for memory argument in MDF methods
- fix incompatible plot title in Signal
- handle backslash in channel names
- fix typo in usage example
- fix _iter_to_pandas_ error
- fix and improve _info_ methods

Fixes
- fix missing attribute error in _Signal_ class when plotting surface (map) signals

API change
- _load_measure_data_ argument was replaced by _memory_ argument:
- _load_measured_data=True_ ⇔ _memory="full"_
- _load_measured_data=False_ ⇔ _memory="low"_
- _memory="minimum"_ is new and will use the least possible amount of RAM (see http://asammdf.readthedocs.io/en/latest/benchmarks.html for benchmark results)

Fixes
- fix errors in _save_ method
- fix errors in _merge_ method
- fix error in _cut_ method for channel groups with no cycles
- fix mdf 4 _TextBlock_ 8byte alignment
- fix wrong link to sample reduction block in _ChannelGroup_ for mdf 4
- fix append and get in case of mdf 4 TTAB conversions
- fix error in case of mdf 4 TTRANS conversion

Fixes
- fix error in _MDF3_ _save_ method
- fix _select_ method to return the signals in the same order as the channels given
- fix _get_ method when channel group cycles number is 0

Changes
- added _select_ generator method to _MDF_
- added _config_ pacakge level function to handle all _asammdf_ configurations
- use data list and split data block when saving (configurable)

Fixes
- fix mdf v3 POLY Conversion
- fix mdf v4 _DataList_ for Python 2
- PEP8 improvements