* refactor: Update parsers/base.py for Python3
* style: Black
* refactor: Remove mime type check from FileParser
* refactor: Validate that submission is UTF-8
The mime check distinguished us-ascii from UTF-8,
but as far as I can tell the code relying on it
treated both as equally valid.
* feat: Clear error when file is not valid XML
* chore: Remove unused import
* test: Update tests to match changes
* fix: Count bytes starting from 1
* test: Add tests of FileParser validations
* fix: Fix / simplify regexp
* test: Test error caused by bad XML submission
---------
Co-authored-by: Robert Sparks <rjsparks@nostrum.com>
