Added Concurrency to speed up the process.

[xalgord]

Added a concurrency feature because it was taking a lot of time when supplying a list of URLs. Now we can adjust the maximum concurrent requests in the (core/checks.py) as shown below:

with concurrent.futures.ThreadPoolExecutor(max_workers=10) as executor:

The default is set to 10.

Also made some improvements to plugin.py.

Below is the proof of its working. (tested on Portswigger lab by placing the URL between Vulnweb URLs in a txt file.)