http server C examples

[barbieri]

Similar to #726, we should provide example for the most common http request handler (server) usages. Please base the examples on those available for other technologies, trying to be as simple as possible in comparison.

Suggested references:

• https://docs.python.org/3/library/http.server.html
• http://golang.org/pkg/net/http/
• https://nodejs.org/api/http.html

Please document the src/lib/comms/include/sol-http-server.h using doxygen and take care to add examples snippets in the sol_http_server_register_handler doc. Add a wiki page with walk through, these may include snippets from the actual sources in the tree.

[ceolin]

Added samples and doxygen doc, snippets is still missing.