#134 Add multithreading syntax support to JML tools

[Gary T. Leavens]

Add multithreading support from the ECOOP 2005
paper to the JML tools. As discussed, we would first:

1. add the syntax and get the parser to work
2. add type checking support
3. Write examples of client code and investigate
reasoning
4. Work on the formal semantics
5. Implement some checking in the RAC.