Nansat

- New mapper: mapper_metno_hfr.py
- Add nansat.utils module

Update the sentinel1_l1 mapper to set the 'entry_id' metadata attribute

- Bugfix in domain.py
- New version of the base Docker image with updated pythesint

* Cartopy replaces Basemap
* New API for write_domain_map()
* New function distance2coas()
* Automatic PyPi deployment on Travis

Automation improvements:
- the docker images are built in Travis CI
- the code for the `nansat_base` image has been moved to the [docker-nansat-base](https://github.com/nansencenter/docker-nansat-base) repository
- the docker images are now available in the [nansencenter](https://hub.docker.com/search?q=nansencenter&type=image) organization in the Docker Hub

Update of automatic generation or docs at ReadTheDocs