Implementation of a test strategy for parsers.

Parser

* A typo has been fixed in the grammar.
* The list of allowed start rules has been completed with other rules that should be tested directly.


Test utility

* A test utility (test/node_modules/parserTester.js) has been added. It allows to test a parser.


Tests

* test.js: it is the test file that mocha runs.
* Tests for the HTML parser have been added.

Close #1