Hepdata-validator

What's Changed
* Reinstate support for Python 3.6 by GraemeWatt in https://github.com/HEPData/hepdata-validator/pull/54


**Full Changelog**: https://github.com/HEPData/hepdata-validator/compare/0.3.4...0.3.5

What's Changed
* Drop support for Python 3.6
* Don't check data file size for old schema versions (closes 53)
* "Invalidate case of only independent_variables" by GraemeWatt in https://github.com/HEPData/hepdata-validator/pull/51
* "Changes for related data update" by ItIsJordan in https://github.com/HEPData/hepdata-validator/pull/52

New Contributors
* ItIsJordan made their first contribution in https://github.com/HEPData/hepdata-validator/pull/52

**Full Changelog**: https://github.com/HEPData/hepdata-validator/compare/0.3.3...0.3.4

* Add check for extended attribute files ([PR](https://github.com/HEPData/hepdata-validator/pull/44), thanks to riga).
* Fixes for LibYAML issues ([PR](https://github.com/HEPData/hepdata-validator/pull/47) fixes [issue](https://github.com/HEPData/hepdata-validator/issues/45)).
* Added file size limit for data files ([PR](https://github.com/HEPData/hepdata-validator/pull/48) fixes [issue](https://github.com/HEPData/hepdata-validator/issues/43)).

Miscellaneous bug fixes ([PR](https://github.com/HEPData/hepdata-validator/pull/41)):

- Invalidate non-numerical errors ([issue](https://github.com/HEPData/hepdata-validator/issues/39)).
- Catch and ignore exceptions in additional checks if already schema errors ([issue](https://github.com/HEPData/hepdata-validator/issues/40)).
- Fix check of `cmenergies` given as a range to allow more than 1 decimal place ([issue](https://github.com/HEPData/hepdata-validator/issues/42)).

Check schema version before checking whether all files are included ([PR](https://github.com/HEPData/hepdata-validator/pull/38)).

* Drop support for Python 2.
* Many bug fixes to schema and additional checks (see [PR](https://github.com/HEPData/hepdata-validator/pull/32)).
* Bump native HEPData schema version to 1.1.0 after these changes.
* New CLI `hepdata-validate` to replace and extend [`check.py`](https://github.com/HEPData/hepdata-submission/blob/master/scripts/check.py) script.
* New `FullSubmissionValidator` class now used in main `hepdata` web application.