Cleanups to RPC code.

This is extracted from a significantly longer RPC change that I put down a couple of weeks ago.

It deletes some unused code, uses Issue and Book a little more, and fixes some long lines and indentation.

Feel free to use this or ignore it!
I'm not convinced either - I just wanted to remove this feature from the main RPCHandler code because David's the only one who ever uses it.  :-D

The file as it is follows the naming convention:  the function doFoo() is in the file Foo.cpp.

The idea is that those free functions will eventually become a class called ripple::RPC::Foo in files Foo.h and Foo.cpp.