Sfftk-rw

added methods for handling notes to `sfftkrw.SFFSegmentation`

Bugfix and minor improvements

Fixed a bug which affected encoded data (lattice, vertices, normals and triangles).

* reverted presentation of `SFFVolume` subclasses to be ordered as (rows, cols, sections)
* now we store encoded data as unicode strings instead of bytes; otherwise, on export we write string with `'b"..."` formatting
* writing to JSON and HDF5 is not raw bytes but Unicode string
* version bump: v0.6.1.dev0

* `-x/--exclude-geometry` for JSON output
* `--json-sort` and `--json-indent <+int>` to control JSON output
* now links to h5py documentation should work
* changed interface for v0.7.0 adapter HDF5 methods in line with sfftk-rw v0.6.0.dev0 changes
* now `args` passed through all classes for command-line contol/features

* clean up of documentation to include correct examples, adapters and generateDS API
* now `from sfftkrw import SFFSegmentation` or `import sfftkrw as sff`
* new images for data model page
* new module `sfftkrw/conf.py` for settings; removed `sfftkrw/api.py`
* added new data files

This is the first release to work with EMDB-SFF v0.8.0 files in addition to v0.7 files. When reading
the API to use is determined from the version attribute. However, creating new files will only
be of v0.8.0.

* new `sfftkrw.api` provided a short path to v0.8 adapter e.g. `sfftkrw.api.SFFSegmentation`
* documentation improvements
* changed entry point to `sff` (from `sff-rw`)
* added references for Python version compatibility: `_FileNotFound`, `_classic_dict`
* added missing field `attribute` to shapes
* changed `SFFSegmentation` container attributes to `*_list` e.g. `segment_list` instead of `segments`.
However we retain `segments` as a property for backward compatibility.
* signature of HDF5 conversion methods (`as_hff` and `from_hff`) is now `*(parent_group, args, name=None)`
by default
* refactored `SFFSegmentation.from_file`
* new `SFFSegmentation.to_file` which is an alias for `SFFSegmentation.export`
* added test data under v0.8 schema

List validations

* schema/base.py: `SFFListType` uses `min_length` attribute to check that minimum length constraint is satisfied
* schema/adapter.py: `min_length` attribute set for `SFFPolygonList` (1) and `SFFVertexList` (3)
* added unit test for the above
* deleted config stub file
* version bump: v0.5.2.dev1