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.
Merge pull request #345 from matthiasbeyer/fix-json_deserializer_restart_parsing

Fix JSON deserializer for restarting parsing