set "0.0.0.dev" as version number on master branch

that way it's clear that installations from a certain commit state are
no release version installations and in addition any version comparison
will prefer proper releases.

Author: megies

pySW4/__init__.py

@@ -26,7 +26,7 @@
 """
 from __future__ import absolute_import, print_function, division
 
-__version__ = '0.2.0'
+__version__ = '0.0.0.dev'
 
 from .core.image import read_image
 from .plotting.drape import drape_plot