Add OP_CAT

[altafan]

Opcode for concatenating bytes.

[tiero]

suggestion: syntax-wise would be fine to use + and/or .concat(toAdd: Bytes)

• + on parsing step, would need to distinguish between the types of the literals of the variables in the binaryExpression ie. Integer should instead use OP_ADD, for an arithmetic operation.
• .concat it should become a callExpression with a dot style signature: this needs introduction of variables first

It seems + could b easier to start with