Parameter CRPIX to the resample step should be 1-based following FITS WCS convention

[stscijgbot-jp]

Issue JP-3823 was created on JIRA by Mihai Cara:

Documentation for the resample step does not specify indexing convention for the CRPIX parameter (custom WCS). Documentation should be updated that CRPIX value is 1-based just like in the FITS WCS standard AND stcal code should be updated accordingly. Currently the code in _calculate_offsets() is written with the assumption that CRPIX is 0-based. This can create inconsistencies and confusion.