feat: support user-defined formats

[ibezkrovnyi]

resolves #1

• usage examples are in 'src/examples' directory
• format is associated with extension. File extension can be set explicitly with square brackets or if there are no square brackets - extension is taken from file
  • package.json - detected '.json' extension
  • .eslintrc [.json] - explicitly set '.json' extension
• supports 3 options formats:

simplified

{
    ".eslintrc [.json]": (content, options) => ...
}

explicit with 'files' property

{
  "files": {
    "package.json": (content, { dir, manifest, file, resolvedPath, _writeProjectManifest }) => ...
  }
}

with user-defined formats

{
  "files": {
    ".somefile [.csv]": () => ...
  },
  "formats": {
    ".csv": createFormat({ ... })
  }
}

[zkochan]

I am not sure why you have bumped the version in the PR. Now I released 0.2.0

[ibezkrovnyi]

I am not sure why you have bumped the version in the PR. Now I released 0.2.0

Apologize for the accident, I assume if there is no configured changesets in the package.json#scripts, version bump has to be done manually.