Add defang function

[rshipp]

Add a defang function that accepts a normal URL/domain/IP and returns a defanged version.

Example input/output:

Input	Output
http://example.com/path.ext	hxxp://example[.]com/path.ext
http://example.com/	hxxp://example[.]com/
example.com	example[.]com
127.0.0.1	127[.]0[.]0[.]1

I need this for ThreatIngestor, makes the most sense to include it here.