SIX 2.2.7 (SIX CSM plugin 1.1.3)

• Added Python convenience methods to convert six::DateTime to a Python datetime object
• Fixed bug in CPHD 0.3 reader that did not properly handle reading 16-bit integer types without a scale factor
• Fixed bug in CSM implementation for parsing both file and NITF ISDs (prevented plugin from being functional)
• Added a series of CSM tests that call the CSM plugin directly rather than going through vts
• Fixed bug in how SICD CSM plugin treated pixel coordinates. CSM defines 0,0 as the upper-left corner of the pixel whereas the SICD documentation defines 0,0 as the center of a pixel. The SIX CSM plugin was previously not accounting for this difference which was resulting in a half-pixel discrepancy in all measurements.
• Significant portions of the Matlab SAR Toolbox's SICD validator were added to SIX. This can be run via check_valid_six or validate_sicd.py. This ingests a SICD and reports any inconsistency in the metadata that is found; this can be useful for SICD producers to ensure they are filling out fields properly as well as SICD consumers to ensure they are receiving well-formed SICDs.