Some 1.3/1.4 syntax specifics are not reflected in parser

[asedunov]

• No error message on invalid ASM syntax since 1.2
• "unwind" is supported in ASM options since 1.2.1 (crystal-lang/crystal@0dc389f)
• Splats in multiple assignments since 1.3 (crystal-lang/crystal@9e52bc9)
• Explicit return types in proc literals since 1.3 (crystal-lang/crystal@fe810b3)
• Parser error with newline in parenthesized expression is fixed in 1.4 (crystal-lang/crystal@8d3155e)
• Proc pointers with global path and top-level method references are supported since 1.4 (crystal-lang/crystal@40d7a2a)
• Generic types with empty type argument list are supported since 1.4 (crystal-lang/crystal@68617c8)