Korean support addition

[turbobit]

This pull request aims to add Korean support in lunr-languages list.

What i did

• Add Korean support
• [x] except Japanese, all the lunr.<language>.js files are built from build/lunr.template
  • [x] If lunr.template does not fit your needs (for example for non-latin characters), just copy any lunr.<language>.js file and start modifying
• [x] you must also test your new language
  • [x] go to test/testdata and create a new file, then link it to VersionsAndLanguagesTest.js
  • [x] make sure you cover many testcases (wildcard, stemming)
  • [x]
  • [x] your tests will automatically be run on all the Lunr versions
• [x] add the new language to README.md
• [x] re-build the files (check section below)
• [x] open a Pull request. Make sure you include everything needed in the pull request (check below)

[MihaiValentin]

Thanks @turbobit for the contribution!