Upgrade the Apex parser used by the engine

TODO: Explain that we rely on a Force.com IDE component, point to our extensive discussions, mention that it is a closed source jar but might become real open source. Mention that it is still SNAPSHOT and therefore can't be pulled in a Maven dependency yet. Explain that people might want to check the status of the parser every Salesforce.com release to see if there are new node types or other stuff. Point them to the explanaition of Nick Check on how to discover the internals of the jar in Eclipse. Show where to replace what in pmd to use a newer jar.

As mentioned at the Add or improve existing PMD rules page we are using the parser of the Force.com IDE to parse Apex source code into abstract syntax trees. This jars are currently closed source but we are allowed to use them as they might become real open source some day. You can find more information about that here.