Fix a bug in reporting invalid pixmap values

See #85 for more details.

Fix bug in interpolation used by the square kernel

Fix a bug in the interpolation algorithm used by the 'square' kernel that resulted in shifts of the resampled image typically by 0.5 pixels compared to the location indicated by the WCS - see #82 and #83 for more information.

Bug Fix: Correct handling of 0-weight pixels

Fixes an issue due to which 0-weight input pixels may still contribute to output image when corresponding output pixels do not have a value previously set (i.e., their weight is 0).

1.13.3

Changes in this release:

• Remove Cython as a runtime dependency [#72]

1.13.2

• Specify oldest-supported-numpy in pyproject.toml so that the built C
  code has the widest possible compatibility with runtime versions of
  numpy. [#60]

• Fix a memory corruption issue in interpolate_bilinear() in
  cdrizzleblot.c which could result in segfault. [#66]

• Fix a context image bug when drizzling more than 32 images into a single
  output. [#69]