Added JSON Lines and Cookies

[tr3ss]

Hi Corben,

Thanks for sharing this tool with the community!

I needed a few things so I added them. If you think they're useful, feel free to merge :-).

1. JSON Lines
   Sometimes a js file is hosted on a different domain than the one in the input file, so when having many source URLs it was difficult to know which URL the finding originated from. I implemented the -jsl flag that prints the output in JSON Lines, containing the source URL as well.
   For example:
   

2. Cookies
   I saw this was a requested feature so I implemented it.

3. Regex tweak

r := regexp.MustCompile(`[(\w./:)]*\.js`)

Not sure if this was intended but initially it also matched js and not only .js.
So strings like blajs were matched as well.

4. README.md
   Changed the install command to use go install instead of go get and added the new flags.

Cheers! :-)