Res2df

* New module: pvt. Parses PVT data, and can also write PVT include files from dataframes
* equil module supports more keywords, and can write include files from dataframes
* satfunc module can write include files.
* Documentation upgrade, dedicated pages for most modules
* grid module can export grid parameters to include files
* nnc module can write EDITNNC data
* Py3 bugfix for gruptree
* Refactored dataframe parsing from deck, easing addition of support for more keywords.

Bugfix release.

* Changes necessary to work with opm-common testing/2020.3/rc1.

Bonus feature addition: equil.df has added the EQLNUM column.

Ported from using sunbeam for DATA-deck-parsing to using opm.io

Sunbeam has been discontinued and moved into opm.common, with a name change and slight API syntax change.

libecl has been added to PyPi, and is now in requirements.txt

Bugfix release.

* Fix bug grid.df() when only rst vectors are asked for
* Fix bug with empty GRUPTREE
* Fix bug in pillars causing implicit grouping from ecl2csv

Added a new submodule, 'fipreports', for extracting FIP report tables in PRT files from Eclipse.

Defer loading of treelib until needed.
* No longer necessary to have treelib installed in order to import ecl2df, only when this tree-functionality in gruptree is requested.