Implemet hashing

[dovudo]

Is your feature request related to a problem? Please describe.

I'll fix a problem of duplicate files.
This solution is simple and good for first issue.

Describe the solution you'd like

Hash files by "xxhash" algorithm, because it's pretty fast algorithm.

• Make hashing each file.
• Add hash to store or txt file in main directory.
• Check hash of every downloaded file with hash store.
• Skip same files.

Additional context
Xxhash benchmark