Allow multiple OR clauses without brackets

Since HIVdb 9.2, there have been conditions like 33i OR 34i OR 35i, which were breaking in pyvdrm, because only binary OR conditions were expected.
This release generalises OR clauses and allows for multiple OR clauses without brackets.

Filter VariantCalls

Remove empty positions when creating VariantCalls.

Raising Exceptions

Change from returning None in scores to raising exceptions.

Negative variants

Replace NOT A10AC with A10!AC.

Flags and Constants

Add features for mutations that trigger flags instead of numeric scores, and rules that are always triggered without any particular mutation.

Negate

Fix a bug with NOT scoring rules.

Scoring

v0.0.1

Include wild type in score residues.