Add Sketchup::Http::Request and Response Tutorial and Example

[DanRathbun]

Add a Tutorial and Example for using the
Sketchup::Http::Request and Sketchup::Http::Response classes.

The little blurbs of sample code in each method, do not stitch together well into an example.

See Ruby docs for standard lib class Net::HTTP for example ideas:
http://ruby-doc.org/stdlib-2.2.4/libdoc/net/http/rdoc/Net/HTTP.html

Ref public forum thread:
New HTTP Request/Response Help