Handling of dicom tags previously not managed

WaveformSampleInterpretation
WaveformBitsAllocated
WaveformBitsStored
ChannelBaseline
ChannelSensitivityUnitsSequence
Requirements out of setup.py

Something goes wrong if requirements are installed by setuptools, so we
suggest to install them via 'pip install -r requirements.txt'
requirements.txt missing from previous commit
Update README.md
Update README.md
Update README.md
Fixes #1
ECG.__init__ now has only one source argument

ECG.__init__ source argument can be:
 * a dict of stu, ser, obj for WADO sources
 * a filename
 * a (c)StringIO buffer