0.9.0 December 26 2019

• Fix to avoid duplicate images being copied to an libxlsxwriter file. Excel
  uses an optimization where it only stores one copy of a repeated/duplicate
  image in a workbook. Libxlsxwriter didn't do this which meant that the file
  size would increase when then was a large number of repeated images. This
  release fixes that issue and replicates Excel's behavior.

  Note, that this change adds a dependency on the Openwall MD5 library,
  which is now included with the libxlsxwriter third party source files. It is
  possible to compile libxlsxwriter without this library, and thus getting the
  older behavior, by passing USE_NO_MD5=1 to make.