v2.0.0: Made `plainroll` work for other d20 games

Main change is that plainroll has some features added to work with other common game rules. Specifically was aiming for 13th Age, but should be useful for D&D and other D20-based games.

What's Changed

• Strip out cheating code. by @freiheit in #112
• plainroll changes:
  • Adds up the total of all the dice results
  • Looks for any number of +N and -N on the roll (like d20 +5 or 4d8 +4 -3 +2) includes that in the math
  • When roll has a single d20:
    • Calls out that nat 1 is likely a fumble
    • Calls out that nat 20 is likely a critical success
    • Calls out that nat 2 is hit for dual-wielders (13th Age rule)
    • Calls out natural even and odd

Full Changelog: v1.3.0...v2.0.0