Add CondFormats' serialization code generator

Please note: I am adding clang's Python bindings at:

  * CondFormats/Serialization/python/clang/

For the moment I put them here to have everything required in the BOOSTIO branch (i.e. works out of the box), but we should have those automatically installed with the LLVM external in production, i.e. these ones:

  * https://github.com/llvm-mirror/clang/tree/master/bindings/python/clang

If you think having the bindings available to Python right now in 7_1_X for everyone might be a good idea, then hold this pull request until we have them and I will update the pull request. See issue 421 at cmsdist:

  * https://github.com/cms-sw/cmsdist/issues/421