Merge pull request #80 from jjhelmus/master

EXAMPLES: Added a number of examples to the documentation
Merge pull request #83 from jjhelmus/master

Various small enhancements and bug fixes
Merge pull request #84 from jjhelmus/master

ENH: Radar colormaps
Merge pull request #85 from jjhelmus/master

ENH: Faster reading of sigmet files and support for missing rays
Merge pull request #86 from jjhelmus/master

ENH: debug parameter on dealias_fourdd
Merge pull request #87 from jjhelmus/master

Various small enhancements, maintanance, and bug fixed
Merge pull request #88 from jjhelmus/master

BUG: time ordering when reading sigmet files
Merge pull request #89 from jjhelmus/master

ENH: Various command line tools.
Merge pull request #91 from jjhelmus/master

BUG: read_sigmet related bug fixes
Merge pull request #93 from jjhelmus/master

Documentation and default parameter changes suggested by users
Merge pull request #96 from jjhelmus/master

Better Reading of NEXRAD Level II file and other small bug fixes and changes
WIP: new metadata system: sigmet working
WIP: new metadata system: nexrad
WIP: new metadata system: mdv, rsl, cfradial
WIP: new metadata system: cleanup
WIP: new metadata system: FILL_VALUE config
WIP: new metadata system: default metadata
WIP: new metadata system: documentation
WIP: new metadata system: default_config.py
WIP: new metadata system: DEFAULT_FIELD_NAMES