FCPClient: Add skeleton of send functions so I can reference them in JavaDoc
- Because sendSynchronous() will wait for the call to complete at the server, it will also be able to tell whether it succeeded or failed. Thus it should either return a value, which might be a boolean or a SimpleFieldSet with information about the error, or throw an Exception. I decided against passing values because then it would be asymmetric to what is passed in the initial send: Sending can pass a SimpleFieldSet AND a Bucket, receiving the result would only be a SimpleFieldSet OR a Bucket. So we would have to introduce a container for SimpleFieldSet and Bucket to fix that asymmetry. Also, the return value should not be abused for passing heavy amounts of data - sync calls should stay fast to prevent thread pileup. So we better not allow passing any information besides success/failure.