===================
- Drizzlepac code will no longer attempt to delete "original" (WCS key 'O')
resulting in a decreased number of warnings
(see `issue 35 <https://github.com/spacetelescope/drizzlepac/issues/34>`_ ).
- Negative values are now zeroed in the 'minmed' step before attempting to
estimate Poisson errors
(see `issue 22 <https://github.com/spacetelescope/drizzlepac/issues/22>`_).
- Fixed a bug in ``tweakreg`` due to incorrect matrix inversion.
- Improved compatibility with `astropy.io.fits` ('clobber' parameter) and
`numpy` which has reduced the number of deprecation warnings).
- Existing static masks in the working directory are now overwritten and not
simply re-used (see
`issue 23 <https://github.com/spacetelescope/drizzlepac/issues/23>`_).
- Corrected formula for :math:`\sigma` computation in the "create median" step
to convert background to electrons before computations. This bug was
producing incorrect :math:`\sigma` for instruments whose gain was different
from one.
- Improved ``astrodrizzle`` documentation for ``combine_type`` parameter which
now also documents the formula for :math:`\sigma` computation
when ``combine_type`` parameter is set to ``'minmed'``.