v0.3.0

Refactor Error types to clean up names and tuple variants:

• ValidationError to ValidateError
• InterpolationError to InterpolateError
• InterpolationError::ExtrapolationError to InterpolateError::ExtrapolateError
• Error::NoSuchField to Error::NoSuchField(&'static str)

Along with other enum changes:

• Extrapolate::FillValue -> Extrapolate::Fill

Version bump for criterion and rand dev dependencies

Full Changelog: v0.2.7...v0.3.0