Centralise checksumming logic
Use base64 representation for checksums
Document checksummer
Allow checksumming everything
Simplify checksummer usage
Make Checksummer.update private
Do not write Rules file in test
Extend rules collection checksum test
Make checksummer tests more robust
Merge pull request #431 from nanoc/checksummer

Checksummer
Allow all pandoc options to be passed
Merge pull request #433 from nanoc/generic-pandoc-options

Allow all pandoc options to be passed
Merge branch 'release-3.6.x'