Initial 0.6.0 groundwork

[Sythivo]

Closes #104

• Upgrades luau to 0.711
• help command dynamic rework, generates help message in compile time.

Breaking Changes

• luau.parse results casing changes, and locations spans are now vector primitives using x and y field for column, and line.
• Library ffi has been renamed to c, with some changes to the API.

Behavior Changes

• require on blank luau files must have a return value (explicitly nil), previously: when having no returns, zune would have considered that as nil.