move mixins and utils to drugs helper
fix tox:pep8 command
add Proxy metaclasses to DocumentSubheaders
move prefix from subheader to data description
add virtual environment to ignore
add colours to tests if there is rednose installed
update representation of data description
add tests for SIZE subheader
add __repr__ functions to class, implement subheaders parser in case of correct subheader
add test to not print None meta
simplify parse of header, satisfy more tests.
satisfy tests for header parser