Callbacks, repo.xml and full hashes

Fixes

• Numerous optimisations and fixes to tuttle's usage of service APIs
  • download of large files from GitHub
  • read all pages of paged requests to ensure all changes are applied on large changesets
  • no duplicate requests

Features

• Callbacks can be configured. They will run after an incremental update has finished. Two callbacks are packaged with
  tuttle: test and check-version
  • test is only for testing purposes
  • check-version will first check if an expath-pkg.xml was updated and 2. then register the changed metadata with exist

BREAKING CHANGES

• The full hash is now used everywhere within tuttle and also returned from all api endpoints. The shortened hash can be of various length and is therefore not stable enough.
• If a repo.xml is found in the repository then that is used to store the commit id (or hash) and commit time.
  Falls back to the gitsha.xml only if no repo.xml is present. Will start using repo.xml whenever it becomes available.

New Contributors

• @DrRataplan made their first contribution in #75
• @duncdrum made their first contribution in #22
• @line-o made their first contribution in #28
• @dependabot made their first contribution in #39

Full Changelog: v1.2...v2.0.0