Implement Rserve 'eval' command

It's really CMD_serEval (0xf5), not CMD_eval (0x03), but from the
user's standpoint it doesn't matter.
Handle either an open IO::Handle or server name/port in evalRserve
Create unit tests for 'evalRserve' that use a live Rserve server
Write the documentation for 'evalRserve'
Implement object methods for Rserve communication
Use different ways to construct an Rserve object to test

- no-arg constructor
- server name
- handle to the server connection
Update the MANIFEST
Increase version to 0.04