Hydropandas

Before this release the version numbering was not consistent, with different numbers for releases and pypi. Now this has been fixed.

Apart from this the code-base has had some improvements.

Rename package from observations to hydropandas. Also adding some minor improvements in reading data.

fix some bugs for reading knmi files.

Fix setup.py to include required data files for KNMI stations.

Major update with lots of changes:
- Cleaned up code-base
- Moved a lot functionality into extensions, i.e. `obs.GroundwaterObs.geo.get_lat_lon()`. Available extensions are: `geo`, `gwobs` (groundwater observations), `stats` and `plots`
- New way of dealing with metadata that changes over time.
- Improved IO, more uniform approach for all the different supported data types.
- And many smaller improvements...