add example code and docs to demonstrate matching data: and tel: URLs

[GoogleCodeExporter]

There is no existing documentation on how to allow data: and tel: URLs.  Add an 
example that demonstrates how HtmlPolicyBuilder.allowUrlProcotols can be used 
with data: and tel:.

Original issue reported on code.google.com by mikesamuel@gmail.com on 21 Jan 2014 at 4:04

[jmanico]

Bump to revisit. Mike, perhaps just give me one complex example and I'll use it to flesh out the docs.

[pickle-weasle]

Can't this be achieved with just
this.policy = this.policy.allowUrlProtocols("tel","data");
In the readme there is the following:

PolicyFactory policy = new HtmlPolicyBuilder()
.allowElements("a")
.allowUrlProtocols("https")
.allowAttributes("href").onElements("a")
.requireRelNofollowOnLinks()
.toFactory();
String safeHTML = policy.sanitize(untrustedHTML);

It's hardly much of a stretch to figure how to change that for other protocols.
Could this be closed?

[DavesMan]

Can't this be achieved with just
this.policy = this.policy.allowUrlProtocols("tel","data");
In the readme there is the following:

No. I have allowUrlProtocols("mailto", "javascript", "tel", "https") and this allows https and mailto. But tel & javascript gets stripped.