PL/0' compiler from https://www.ohmsha.co.jp/book/9784274130137/
- add tests.
- make it capable of compiling like this
$ ./pl0d ${SOURCE_FILE}
- add option to output intermediate code
compile on Docker.
$ docker build -t compiler ./
$ docker run -it compiler make pl0d
run binary
$ ./pl0d
enter source file name