new formula: ODB C++ Object-Relational Mapping(ORM)

Now ODB compiler is built from source.

The remain problem is I must use this command to install the formula
brew install odb --env=std since I use homebrew gcc.

Can I avoid it?

@adamv @mikemcquaid @mistydemeo 
Can this test be modified to do something more substantial than e.g. `--version` or `--help`? See `cmake.rb` for an example of an application formula with a good test and `tinyxml2.rb` for an example of a library formula with a good test. Thanks!