+Add locations of all well-known WSR-88D stations. (Source: Weather Climate Toolkit)
+Add capability to read old nexrad-cdm archive. (Read lat,lon,alt from config)
*It is more reasonalbe to always set reference altitude to sea surface when mering multiple radars. (Change in grid_mapper.py)
ENH: location set when reading old NEXRAD files.

Reading CDM converted NEXRAD files which do not contain the
latitude, longitude and altitude will not fill these parameters
in from the known locations of the NEXRAD stations.
DOC: documented nexrad_common module
Merge pull request #137 from jjhelmus/pr_126

ENH: Location determined when reading older NEXRAD files