Polish v1 & v2 documentation

[andir]

With the merge of #166 we are in a bit of a weird situation with the documentation.

The documentation was updated for the changed API that was developed as part of support the version 2 of the NPM lock files. Somewhere along the path it was decided that these new changes should be exposed as a dedicated attribute. This will keep the old (called v1) code alive and we can introduce the new features as v2.

• Proof read the API.md
• Split v1 documentation into API-v1.md
• Move the v2 documentation into API-v2.md
• Make the API.md describe that we expose two versions of the api and link to those

[zmrocze]

im polish so this is very anticipated, would make it way easier to understand. Keep up the good work!