Service release

New features:

• coordinates: SQLite backend for trajectory info data. This enables fast access to this data
  on parallel filesystems where multiple processes are writing to the database. This greatly
  speeds ups reader construction and enables fast random access for formats which usually do not
  support it. #798
• plots: new optional parameter arrow_label_size for network plotting functions to use a custom
  font size for the arrow labels; the default state and arrow label sizes are now determined by the
  matplotlib default. #858
• coordinates: save_trajs takes optional parameter "image_molecules" to correct for broken
  molecules across periodic boundary conditions. #841

Fixes:

• coordinates: set chunksize correctly. #846
• coordinates: For angle features it was possible to use both cossin=True and deg=True, which
  makes not sense. #857
• coordinates: fixed a memory error in kmeans clustering which affected large data sets (>=64GB). #839
• base: fixed a bug in ProgressReporter (_progress_force_finish in stack trace). #869
• docs: fixed a lot of docstrings for inherited classes both in coordinates and msm package.