Allow RVICHIST_MFILT option to include year, month, or day string value.  This change dynamically determines the number of time samples in each output file based on the sring value.  Closes issue #5.
Support for partially full history tapes.  Does not inclue values between updates of out_data structure (this will require writing a history state file
Merge branch 'develop' into feature/output_file_chunks

Conflicts:
	rvic/core/history.py