0.7.3

• Updated error semantics of os.remove & os.rename to match Lua's again (return false instead of raising error), Pluto's 'io' versions of these functions remain unchanged
• Fixed extends not copying over metamethods
• Fixed "memory allocation error: block too big" when parsing --[[]]
• Fixed allowing function calls to primitives, causing ambiguities with exprstat after assignment
• Fixed string.upper & string.lower delimiting on '\0'
• Some other improvements and bugfixes