Update .gitignore for Gradle / Eclipse.
Add .classpath to .gitignore.
Add a first skeleton for the compiler.

The grammar in src/main/sablecc/minijava.sablecc is currently just
a grammer for some basic arithmetic expressions. It was taken from
[1].

The Main class creates a lexer, parser and then parses input from
a file specified on the command line. It then visits the abstract
syntax tree with a PrintVisitor to print it.

So, in short: Lots of work before this is a MiniJava compiler :)