Add rate limiting feature

[timkent]

Currently VHostScan will fire off requests as fast as possible, this is probably not ideal for all situations.

Rate limiting or a configurable pause between requests would be a good feature to add.

[cryguy]

can we use external library's for it? or do we not want any external libs?

[codingo]

@cryguy Depends on the library - any suggestions? I think it could be done a natively but I'm open to a library if it leads to a better end result.

[cryguy]

am looking at - https://pypi.python.org/pypi/ratelimit right now

edit - doing it natively will be easier i guess

[timkent]

Thanks @cryguy for looking at this!

If you do use an external library, try to preference ones that are packaged in Debian if possible, as we want to try to package this up eventually to make it really simple to install in Kali.

Obviously don't discount others if they are a better fit, but please factor this in.

[grimd34th]

#40
Added a time.sleep to the function call with a default of 0, uses python standard libraries so no additional deps

[cryguy]

#39 added ratelimit and documentation for ratelimit func

[codingo]

@cryguy @grimd34th Happy for open discussion on which approach you feel is better (#39, #40). I don't believe there's too many edge cases here that either wouldn't solve but I'm happy to be proven wrong!

[codingo]

Closed with #40, #44