The "builtins" prefix for the flake8-builtins options is redundant and is inconsistent with other options like allowed-unused-imports or allowed-markup-calls.

• Rename builtins-allowed-modules -> allowed-modules
• Rename builtins-ignorelist to ignorelist

Although we can tackle this in 0.9 release, I'd say we do the rename (maintaining backwards compatibility) after the 0.9 release and hard deprecate in 0.11.