Feature/c++11

#### Summary:

Updates parser for C++11 compatibility and removes C++03 unsequenced warnings from clang++.

#### Intended Effect:

Compile in C++11.  No warnings compiling in C++03.  Remove undefined behavior due to unsequenced updates (assuming warnings in clang++ weren't false positives).

#### How to Verify:

Compile `stanc` in `clang++` (included in unit tests) on latest Xcode and notice there are no more warnings.  Compile with `-std=c++11` and note that it works.  Also no warnings in `g++`.  

#### Side Effects:

None.

#### Documentation:

Not user facing.

#### Reviewer Suggestions:

Daniel, because he'll be pickiest for tests and might have the patience to look through the massive diff resulting from the extensive parser changes to semantic rules and the large number of new tests for warning and error messages being thrown accurately.

#### Acknowledgments

Thanks again to Robert Goedman for figuring out the Boost iterators for the C++11 part of this pull request.