Replace RETRIEVE_MESH with RETRIEVE_RESULT.

As we move away from returning just meshes as the result of a worker task,
the name for the command needs to be generalized.
Deprecate returnMeshResults in preference for returnResult.

As we continue down the road of not always returning meshes, we need to move
to more general names.
Update the readme to not used deprecated methods.
update the integration tests to not use deprecated methods.
update the worker examples to not use deprecated methods.
The server method that deals with RETRIEVE_RESULT now has a matching name
Keep working around testing non blocking calls in threaded environment.

Since we keep testing non blocking methods in a system that has numerous
background threads do work. So we have to wait for the work to be done, but
we don't want to use blocking calls since we are trying to verify the non
blocking versions.
Update the tetgen and triangle workers to use the new remus register call.
Remove a duplicate main function in the tetgen worker example
Merge pull request #154 from robertmaynard/get_examples_to_compile

Get examples to compile
Merge pull request #153 from robertmaynard/stable_integration_tests

Keep working around testing non blocking calls in threaded environment.
Merge pull request #150 from robertmaynard/better_RETRIEVE_MESH_name

Replace RETRIEVE_MESH with RETRIEVE_RESULT.
Merge pull request #151 from robertmaynard/deprecate_returnMeshResults

Deprecate return mesh results
devirtualize remus::worker as it should never be derived from.

You should be using remus::worker in a composition manner instead
of using inheritance.
Make sure the example workers prefer composition over inheritance.