Improve testings / provide examples

[mnlevy1981]

Testing should be split into two directories:

1. regression tests -- basically all of the tests we have now are regression tests
2. unit tests -- testing at a very basic level. Do things like ensure cvmix_put and cvmix_get write to the proper place, the initialization routines provide the expected default values, etc etc.

Also, should provide some light-weight examples for both stand-alone single column cases and (if possible) an outline of steps needed to import into a pre-existing ocean model.

Random thoughts:

1. Examples could build libcvmix.a out of src/shared/ and then link a simple driver from each subdirectory
2. src/drivers/ could be thought of as src/reg_tests/
3. What's the best way to build unit tests? All in single Fortran file (that, like examples, would only depend on libcvmix.a)? Should we require pfunit?
4. We should really look into automating the regression tests across a handful of machines / compilers.