First class support for functions in Spasm

[dtrendafilov]

Design and implement first class support for functions in Spasm

• functions as values
• support for closures

Functions as values

The ability to have high-level - get functions as arguments, assign functions to properties, etc

Support for closures

The ability for functions to return other functions and to use variables from the enclosing scope

• May require new opcodes
• How and when to create a closure?
• How to share closures between functions ?