Add support for Jest

[hassankhan]

Feature request description

It would be awesome if depcheck could exclude Jest as well as any transformer modules as per the documentation.

Code snippets (if applicable)

How the dependency is used (if applicable):

// jest.config.js
"transform": {
  ".(ts|tsx)": "ts-jest"
},

How the dependency is listed in package.json (if applicable):

package.json snippet here
please include the section name (e.g. devDependencies, dependencies)
{
  "devDependencies": {
    "jest": "^23.0.0"
  }
}

[mnkhouri]

Hi @hassankhan, thank you for the detailed suggestion! Based on the documentation you linked, the detection seems fairly straightforward, so I think it should relatively easy to add this support as a "special", for example like babel.

If you have the time to try out a PR for this, it would be greatly appreciated! No problem if not, of course -- hopefully we can get to it soon