The names of immutable `bytes()` and mutable `bytearray()` should be changed to `ibytes()` and `mbytes()` respectively

[bytes()](https://docs.python.org/3/library/functions.html#func-bytes) is immutable and [bytearray()](https://docs.python.org/3/library/functions.html#func-bytearray) is mutable so their names should be changed to `ibytes()` and `mbytes()` respectively so that we can easily and intuitively understand them.