Ecl2df

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.

Feature release:
* New pillar module, for computations on cornerpoint pillars volumes, statistics, and fluid contact determination over time.
* ecl2csv subparser 'smry' renamed to 'summary'
* ecl2csv summary supports specifying start and end dates.
* compdat module can merge zone-names and INIT-vectors
* Docs upgraded

Changes:
* Breaking API change: Submodules under ecl2df has "2df" removed from their name. Backwards compatibility only for satfunc2df and compdat2df.
* NNC fix, previous version gave erroneous data.
* NNC output can be limited to only vertical pillars (to analyze pinches etc.)
* summary output can include data from parameters.txt
* Stacking option for RST data (by date)
* Add a zone map option, so that K indices can be mapped to a zone string.
* Add function to build a dataframe of cell transmissibility pairs, similar to NNC (no command line tool yet)