v6.0.0

Added

• Child contracts
• Chain.clone
• Chain.create
• Chain.bytecode_hash
• Minor support for variadic functions
• void type that represents an empty type
• Call.fee builtin

Changed

• Contract interfaces must be now invocated by contract interface keywords
• main keyword to indicate the main contract in case there are child contracts around
• List.sum and List.product no longer use List.foldl

Removed