make tests, make docs, and more.

A minimal request_hook example.

A sample server that maintains a permutation using CLPFD constraints.

Also showcase the use of simple_jsonrpc_server.pl features, like
logging, and debug JSON-RPC messages for attaching and detaching to
the SPIDER debugger.

Various operations on an integer permutation, represented as a list of
constraint variables.

This code is independent of JSON, JSON-RPC.

Note: The C# code triggers many warnings from the compiler.

A simpler (and safer) version of the server used by the various client
examples.

An easier to use wrapper around jsonrpc_server.pl.

Also, various utilities, like logging and attaching to SPIDER
debugger.

Change state handling.

Change hook story. Now any JSON-RPC request can be hooked.

Change cut story, now can cut deeper than just the most recent choice
point.

Simplified the once/call method template processing.

Notable bug fixes compared to SP 4.7.x:

Server loop left choice point behind on each iteration.

Handle cut that fails, e.g. because of a failing call_cleanup/2
cleanup.