Merge branch 'sb/hashmap-customize-comparison'

Merge branch 'sb/hashmap-customize-comparison'

Update the hashmap API so that data to customize the behaviour of
the comparison function can be specified at the time a hashmap is
initialized.

* sb/hashmap-customize-comparison:
  hashmap: migrate documentation from Documentation/technical into header
  patch-ids.c: use hashmap correctly
  hashmap.h: compare function has access to a data field