Add Additional Generic Url Variables

[wdahlenburg]

This PR attempts to address some of the items in #491 and #927.

This adds the following generic variables that are parsed from the url:

{{Domain}}
{{Path}}
{{Port}}

The {{BaseURL}} and {{Hostname}} variables should remain unchanged in any templates.

I broke out the code in the Make function within v2/pkg/protocols/http/build_request.go and added a generateVariables function. This felt like a more succinct way to handle this.

It should be pretty easy to expand this for anything else, but this seemed like a good start.

[ehsandeep]

thanks a lot @wdahlenburg and creating this PR, @parrasajad is already on this so he might pick it from here or make additional PR, we will keep you updated.

Here is a list of global variables we intend to support:

https://hackerone.com:443/foo?profile=true

{{BaseURL}}		 - https://hackerone.com:443/foo?profile=true
{{RootURL}}		 - https://hackerone.com:443
{{Hostname}}	         - hackerone.com:443
{{Host}}		 - hackerone.com
{{Port}}		 - 443
{{Path}}		 - /foo
{{Scheme}}		 - https

http://104.16.100.52/foo?profile=true

{{BaseURL}}		 - http://104.16.100.52/foo?profile=true
{{RootURL}}		 - http://104.16.100.52
{{Hostname}}	         - 104.16.100.52:80
{{Host}}		 - 104.16.100.52
{{Port}}		 - 80
{{Path}}		 - /foo
{{Scheme}}		 - http

[Ice3man543]

@wdahlenburg Added some more variables as mentioned by @ehsandeep. The changes look good to me, merging the pr! Thanks again for your contribution.