When python mimetype fails(files without extension), fallback to libmagic to determine mimetype based on magic header. Added some extra helper methods in utilities, the image analyze now returns main layer as subname instead of the filename.
srgb
Changed datetime format to iso
Added specific exceptions for metadatastore
Rework Entry points:
 - Adding base class for entry points.
 - Add inspect entry point
 - Work on transcoder entry point.
Switch to argparse.
Work on transcoder entrypoint. Exceptions moved.
More work on entry points. Incomplete still.
Merge branch 'entry_points' of https://github.com/induane/damn-at into entry_points

* 'entry_points' of https://github.com/induane/damn-at:
  Rework Entry points:  - Adding base class for entry points.  - Add inspect entry point  - Work on transcoder entry point.

Conflicts:
	damn_at/entry_points/__init__.py
	damn_at/entry_points/transcode.py
	damn_at/metadatastore.py
	damn_at/run_damn.py
	damn_at/transcoder.py
	setup.py