Enable the server to support development with some helper tools:
You can now request debug information with statistics on how
long execution of a command took, how long it took to serialize
the JSON files, and how big the serialized JSON string is.
Also allow to dump results into a file.
Allow for experimental cmProtocolVersions, which will only ever get
listed if the server was started with the (undocumented)
"--experimental" flag.
Mark current protocol version 1.0 as experimental.
Adds a bare-bones cmake-server implementation and makes it possible
to start that with "cmake -E server".
Communication happens via stdin/stdout for now.
Protocol is based on Json objects surrounded by magic strings
("[== CMake Server ==[" and "]== CMake Server ==]"), which simplifies
Json parsing significantly.
This patch also defines an interface used to implement different
versions of the protocol spoken by the server, but does not include
any protocol implementaiton.