feat: added repository preview (Issue #5)

[kugiyasan]

I got a first working version, however there are a few points to fix before merging this:

• There is a one second delay everytime the program scrapes a new page. I think that throwing mpsc::channel and threads to the problem could work, however I'd be glad to hear some other opinions!
• Files and directories can be easily confused in the preview, I will add a slash at the end of the directories soon, tell me if you have any better ideas (coloring directories with a different color might be another idea).

[Mannan-Goyal]

Yeah, we think that scraping the repository asynchronously is a good idea. Also, the "/" or color thing both work. Great Job!

[kugiyasan]

I think I'm done implementing the feature!

The only flaw that I know of is that I'm creating a new thread for each request. This shouldn't be a problem during normal usage, and it can be mitigated by the use of a threadpool, however this would require implementing ThreadPool ourselves or using a crate for this. I'll let you guys decide on whether or not import a whole crate just for this sake.