ENH: Faster reading of sigmet files and support for missing rays

* Sigmet files are read as speeds similar to RSL using the Cython SigmetFile
  object.
* Sigmet files which contain rays which were not collected are returned as
  proper radar object with the missing rays excluded from the data.
ENH: Two addition to sigmet files reading.

* read_sigmet can now accept a file-like object as the filename parameter.
* 1-byte moments can are now converted by SigmetFile objects.
BUG: fixed reading of sigmet files with ray data to the end of the record
ENH: reading of sigmet files with extended headers
Merge pull request #85 from jjhelmus/master

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

ENH: debug parameter on dealias_fourdd
ENH: add_field and add_field_like methods on Radar object
ENH: info method added to Radar object
MAINT: renamed netcdf to cfradial in functions/classes
ENH: RadarDisplay.plot_ray method.

* plot_ray method added to RadarDisplay class for plotting individual rays.
* RadarDisplay unit tests updated for more complete coverage.
* LP Phase Proc example updated to use new plot_ray method.
* Removed rayplot.py file as functionality now present in RadarDisplay.
MAINT: Removed unused sounding module
BUG: read_sigmet now works with Python 2.6
Merge pull request #87 from jjhelmus/master

Various small enhancements, maintanance, and bug fixed
BUG: time ordering when reading sigmet files
Merge pull request #88 from jjhelmus/master

BUG: time ordering when reading sigmet files
ENH: Various command line tools.

The following command line tools are now available:

* anytocfradial: create a CF/Radial file from any radar file.
* radar_info: print out information about a radar file.
* radar_plot: create a plot for a radar file.
* check_cfradial: check that a file meets CF/Radial standards.

The main setup.py file updated to install the above scripts during install,
and PEP8 cleanup was performed on this file.
BUG: reading Sigmet file with data_type > 58.

Sigmet files which are truncated (end early) can also be read.
Closes issue #90
Merge pull request #89 from jjhelmus/master

ENH: Various command line tools.
ENH: read_sigmet will set sigmet_exteded_header metadata