ENH: beam width parameters when reading RSL files.
ENH: beam width parameters when reading Sigmet files
ENH: beam width parameters when reading MDV files.
BUG: writing cfradial file without instrument_parameters

Writing a Cf/Radial file from a radar object in which the instrument_parameters
attribute is None no longer errors out.
MAINT: Error message when reading nexrad msg1 files
Merge pull request #151 from jjhelmus/master

ENH: beam width parameter included when reading files