* Replace SYSTEM_NAME and other macros with C++ constructs
* Remove RIPPLE_ARRAYSIZE and use std::extent or ranged for loops
* Remove old-style, unused offer crossing unit test
* Make STAmount::saFromRate free and remove default argument
When JSON-RPC and Websocket responses are calculated, the result is stored
in intermediate Json::Value objects and later composed in a single linear
memory buffer before being sent to the socket. These classes support a
new model for building responses that supports incremental construction
of JSON replies in constant time and removes the requirement that all
data returned be located in continuguous memory.
* New JsonWriter incrementally writes JSON with O(1) granularity and memory.
* Array, Object are RAII wrappers for the O(1) JsonWriter.
