Standard python file handle does not fly - update docs

[markusdregi]

The fact that most functions in libecl cannot work on a standard Python file handle, but needs a cwrap.open file handle is severely under communicated. Arguments are named pyfile etc. See EclGrid.save_grdecl as an example.

[pinkwah]

Could we perhaps just extend the functionality so that it can handle Python file handles? They're all the same C stuff under the hood.