Add basic indexer Binary serialization and routes

- add type variable to DocumentWrapper for the implementation
- Binary instances for Index and DocTable
  - requires UndecidableInstances for (HashedDocuments implementation)
    instance Binary (DocumentWrapper e) => Binary (Documents e)
- add routes /binary/save/:filename and /binary/load/:filename
- saves two files for index and doctable
- minor cleanup
Extend .gitignore file (.cabal-sandbox)