Sfftk

Multi-file support for STL files

* docs rebuild
* map, stl: segment file basenames (not full path)
* new multi-file tests for STL and MAP

Bugfixes

* read JSON SFF file for 3D volume correctly

* ``sff prep <command>`` to prepare your segmentation
* ``sff prep binmap`` to bin a CCP4 map file

* Only works with EMDB-SFF v0.7 files. The main feature of EMDB-SFF v0.7 is that 3D volumes are embedded into the
EMDB-SFF file. Previously 3D volumes were only referred to.
* Other EMDB-SFF changes:
* Deprecated filePath attribute
* Transforms can only be of type transformation matrix (deprecated canonical euler angles and view vector rotattion
transforms)
* Segments now have both a name and description
* Added this change log
* EMDB-SFF test data is now split by version
* Update of unit tests
* Utility function ``parallelise()`` for parallel computations (mainly used for decoding 3D volume data)
* Utility function ``rgba_to_hex()``

* Added documentation on extending for external resources
* Replaced ``print`` calls with ``print()`` (prep. for Python 3)
* Deprecated contours as a segmentation representation