Pyhpo

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- Refactored Gene and Disease annotations
- Added proper hashing methods to ``HPOTerm``, ``Disease`` and ``Gene``
- Bugfix for similarity score when one set does not contain any HPOTerm
- 2.6.1: Re-add (Gene/Omim).get method for single gene/disease fetching. Needed in pyhpoapi

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- Added combination methods for HPOset similarities
- Added Matrix module for row/column based operations
- Data update to ``hp/releases/2020-10-12``
- HPO: 15530 ==> 15656
- Genes: 4366 ==> 4484
- OMIM: 7801 ==> 7860
- Negative OMIM: 652 ==> 660
- ORPHANET: 3956 ==> 3989
- Negative ORPHANET: 255 ==> 259
- DECIPHER: 47 ==> 47
- Negative DECIPHER: 0 ==> 0

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- Data update to ``hp/releases/2020-08-11``
- HPO: 15332 ==> 15530
- Genes: 4317 ==> 4366
- OMIM: 7675 ==> 7801
- Negative OMIM: 638 ==> 652
- ORPHANET: 3889 ==> 3956
- Negative ORPHANET: 240 ==> 255
- DECIPHER: 47 ==> 47
- Negative DECIPHER: 0 ==> 0

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- Added GraphIC similarity measure

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- Added Orphanet diseases to Annotation
- Added Decipher diseases to Annotation

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- Reworked BasicHPOSet
- Added omim_diseases to HPOSet
- Added distance method to similarity measurement
- Added equal measurement to HPOSet similarity