5e velocity maneuvers

[phBalance]

• Refactor similar velocity calculation code across the code base.
• In new function return velocity in system units rather than metres (resolves #923).
• Tighten up in combat velocity calculations in cases where the combatant hasn't moved.
• Allow the velocity field of the to hit form to be modified in case it's incorrect.
• Fix v/10 cases for velocity calculations by allowing multiple digits in the regexp.