Nansat

Changelog
* Make correction of GCPs in Sentinel-1 data optional
* Sentinel-1 GCPs correction is based on trigonometry of viewing
* Metadata is unescaped onreading
* WKV retrieval from Pythesint is fixed

Changelog
* Update Sentinel-1 L1 mapper: works in Python 3; corrects GCPs near Greenland; works with the new IPF version
* Mock pythesint in all tests
* Add Appveyor CI
* Create unique temporary files in all Exporter tests
* Bugfixes

Changelog
* Update of tests: PointBrowser tests are made qt5 independent; Exporter tests write temporary files;

Change-log:
* Add Nansat.extend()
* DRY netCDF Mapper
* Fix Envisat Mapper to use open() instead of file()
* Fix Geolocation to take VRT objects
* Add Nansatmap and other issues of backwards compatibility
* Improve links for dependencies in docs
* Fix read-the-docs
* Update conventions of merging/branching in the docs
* Remove using old errors from Nansat and other modules

A major revision of Nansat!

* Works on all major platforms: Windows, Linux and OS X
* Works on Python 3.5 and 3.6 as well as 2.7
* Integrated with PyPi
* Installation is made a lot easier with Anaconda
* All documentation is now available at https://nansat.readthedocs.io
* Major refactoring of the code
* Increased test coverage to 90%
* Removed Mosaic and Nansatmap modules to their own repositories
* Bugfixes

Bug fix in mapper for netcdf-cf files