Install and configure lint-staged

Installed `lint-staged` (1) to run linters against staged Git files to
prevent to add code that violates any style guide into the code base.

The `lint-staged.config.js` configuration file has been placed in
the project root and includes the commands that should be run for
matching file extensions (globs). It includes at least the three
following entries with the same order as listed here:

1. `prettier --list-different` - Run Prettier (GH-37) against
  `*.{js,json,md,yml}` to ensure all files are formatted correctly.
  The `--list-different` prints the found files that are not conform to
  the Prettier configuration.
2. `remark --no-stdout` - Run remark-lint (GH-36) against `*.md` to
  ensure all Markdown files are compliant to the style guide
   The `--no-stdout` flag suppresses the output of the parsed file
   content.

References:
  (1) https://github.com/okonet/lint-staged

Epic: GH-33
Depends on GH-36 GH-37 GH-47 GH-49
Blocks GH-45
Resolves GH-44

lint-staged.config.js

@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2017-present Arctic Ice Studio <development@arcticicestudio.com>
+ * Copyright (C) 2017-present Sven Greb <development@svengreb.de>
+ *
+ * Project:    snowsaw
+ * Repository: https://github.com/arcticicestudio/snowsaw
+ * License:    MIT
+ */
+
+/**
+ * @file The lint-staged configuration.
+ * @author Arctic Ice Studio <development@arcticicestudio.com>
+ * @author Sven Greb <development@svengreb.de>
+ * @see https://github.com/okonet/lint-staged#configuration
+ */
+
+module.exports = {
+  "*.{js,json,md,yml}": "prettier --list-different",
+  "*.md": "remark --no-stdout"
+};