Refactor DNS

1) Move the files below {src,test}/protocols from {src,test}/net.

2) Move classes into the ight::protocols::dns namespace.

3) Remove the leading DNS from names, i.e., DNSResponse -> Response.
Replace ight::protocols::dns::Settings with ight::common::Settings
dns.hpp: tweak example usage
Merge pull request #52 from bassosimone/refactor/dns

Refactor dns code
Add implementation of HTTP response parser
Implement http stream minus error handling
Sketch out API for HTTP client
Rename return value
stuff
Move http in protocols
Fix more stuff and antani