Pip package name problems, attr vs attrs

Finding "import attr" in source, pipreqs reasonably includes:

`attr (0.3.1) - Simple decorator to set attributes of target function or class in a DRY way.`

Whereas I really want:

`attrs (18.2.0) - Classes Without Boilerplate`

What's the right option here?

Could one provide a "package name map file" as a config option?

Something like:

```
# import to package name mapping file
attr: attrs
```

Then specify this on the command line?

Start by tracing how pipreqs resolves imports to package names and how command-line options are defined; the issue names no source files or tests. Compare the proposed attr-to-attrs mapping format with the existing configuration flow, then define completion as accepting a user-supplied mapping and selecting attrs for the attr import without changing unrelated package resolution.

Written by the indexing model from the issue text.