Data-vault

What's Changed
* Performance: use 7z to open files
* Performance: check integrity of a single file on read, not of entire archive
* Fix order of docstring
* Fix compatibility with new IPython version
* Migrate CI to GitHub Actions by krassowski in https://github.com/krassowski/data-vault/pull/19
* Allow to pass with a warning when CRC == 0 by krassowski in https://github.com/krassowski/data-vault/pull/18

- Allow to access methods and attributes
- Do not require variable to be present in namespace to delete it from store

Documentation updates only

Improvements to memory optimisation of imported frames:
- numbers and booleans are no longer categorised (by default, both can be enabled, although the booleans categorisation is unlikely to be ever beneficial)
- memory savings reporting is now disabled by default (can be switched on with report_memory_gain switch)