[#3] Implement hashStore function

[chshersh]

Resolves #3

@int-index check whether this is what you had in mind.

Also, I noticed one thing: generated paths are really ugly and contain weird symbols like this:

8^Äkbx?,þÓ-?à7(ýóóo??÷&âA)i??Ý,?Y²kr+Õ³?bRb??U?¦¹ËÈ«??ÁË??0Cè`o?-LICENSE

Should we do something with it?

[int-index]

We have to avoid control characters like the newline in filenames, so please render the hash in base16 and don't use ByteString.Char8 (it's a bad module, it truncates data)

[chshersh]

@vrom911 @int-index I've updated implementation according to review comments.