Improved the GithubFetcher

The GitHub fetcher is now easier to use and has more possibilities.

Sources can now be taken from:

• Main/Master Branch

{
  "name": "Example",
  "fetcher": "github",
  "source": "exampleUser/example-repo/"
}

• Specific Branch

{
  "name": "Example",
  "fetcher": "github",
  "source": "exampleUser/example-repo/branch/branchName"
}

• Latest Release

{
  "name": "Example",
  "fetcher": "github",
  "source": "exampleUser/example-repo/release"
}

• Specific Release Tag

{
  "name": "Example",
  "fetcher": "github",
  "source": "exampleUser/example-repo/tag/1.0"
}

I also cleaned up some formatting 😛