You can either run the lexer/parser as a standalone unit or as a Unix pipeline.

To get the standalone unit, just run `make Main`. This creates an executable
called "Main". Then you can do `./Main file1 file2 ...`.

To get the Unix pipeline, just run `make`. This creates executables "Lex" and
"Parse" (it also creates "Main" but we don't care about that). Then you can
do `cat file1 file2 ... | ./Lex | ./Parse`.