Rename 'Val' to 'Hylo' (github.com)

A new programming language based on "mutable value semantics" has been renamed from Val to Hylo. It was a frequent complaint that the former name was too similar to other existing languages like V, Vala, and Vale. Mutable value semantics is a new way to efficiently pass around data structures without having explicit references/pointers present in the language and complicating semantics. Pointers are basically relegated to a status of a possible optimization that the compiler can perform at the assembly level.