Add integral arithmetic operation helpers
Add implementation for ws_builtin_cmd_add()
Add implementation for ws_builtin_cmd_sub()
Add implementation for ws_builtin_cmd_mul()
Add implementation for ws_builtin_cmd_div()
Merge pull request #304 from matthiasbeyer/add-arithmetical_commands

Add arithmetical commands
Reset state when finishing the current transaction.
Consume whitespace in deserialize()

deserialize() consumes whitespace at the start of the transaction buffer
on its own.