Clear build warnings
I have desire to clear all build warnings form Nimble, but I'm not sure what to do with deprecation warnings. It seems that Nimble is still being tested against an older version of Nim - [0.19.6](https://github.com/nim-lang/nimble/blob/7c2b9f612e6a42609f28f8f51de4ab6949ced4a0/.travis.yml#L8). Half of the warnings are of this type:
```
Warning: Deprecated since v0.20, use 'initHashSet'; initSet is deprecated [Deprecated]
```
and fixing them will break backward compatibility with an older Nim. Is such compatibility still required?

The other half of the warnings are from the type:
```
Warning: imported and not used: 'sets' [UnusedImport]
```

and they are caused by the new feature for detecting unused imports. I suspect that it will be completely safe to remove them.

There are also some hints for dead code like:
```
Hint: 'getSpecificDir' is declared but not used [XDeclaredButNotUsed]
```

Can I remove such unused functions or they are left intentionally?
