Many references to jgm/commonmark – renamed to commonmark/XYZ

[kevmoo]

Started here #125

CONTRIBUTING.md:9:[github issue tracker](http://github.com/jgm/commonmark.js/issues)
README.md:4:[![Build Status](https://img.shields.io/travis/jgm/commonmark.js/master.svg?style=flat)](https://travis-ci.org/jgm/commonmark.js)
README.md:39:<https://raw.githubusercontent.com/jgm/commonmark.js/master/dist/commonmark.js>,
bower.json:4:    "homepage": "https://github.com/jgm/commonmark.js",
dingus/index.html:30:[commonmark.js](https://github.com/jgm/commonmark.js), the
package.json:10:  "repository": "jgm/commonmark.js",
package.json:12:  "bugs": { "url": "https://github.com/jgm/commonmark.js/issues" },
test/regression.txt:83:Issue jgm/commonmark.js#121 - punctuation set different