Add basic lexer tests.

Test whitespace, operators/keywords, identifiers, integer literals
and some failure cases.

The tests are ignored for now because they would still fail. To make the
tests run, replace "ignore" by "it" in front of the tests.
Remove token class for "import" keyword.

It does not occur in the MiniJava grammar according to the language specification.
Merge pull request #12 from jspam/007-import-unused

Remove token class for "import" keyword.
Merge pull request #11 from jspam/005-lexer-tests

Add basic lexer tests.
Remove options from CLI, add lextest
Merge pull request #20 from soc/topic/cleanup-cli

Remove options from CLI, add lextest