v1.9.3.6

v1.9.3.6

New features:

1. reshuffle some code between ostap.fitting.variables and ostap.fitting.roofuncs
2. reshuffle some code between ostap.fitting.variables and ostap.fitting.rooreduce
3. add serialization/reducing for the graph-like objects
4. fix exampels
5. disable python warning from scipy.signal
6. add decorations for TGraphMultiError type
7. add helper module valerrors

Backward incompatible:

Bug fixes:

1. fix typo in dataset.py. Thanks Dmitry Pereima for reporting the problem
2. fix typo in tmva.py
3. fix serialization for TGraphMultiError type