Remove .npmignore.

We specify the files to include to npm in package.json, so this isn't needed.
src/markdown.js: fix typo in comment.
Rename *.markdown docs to *.md.
Update README.md.

Fix release link and remove empty lines from lists.
Update Changes.md.

* link to the issues and to the authors
* sort issues by number
* a few other minor improvements
Merge pull request #118 from XhmikosR/master

Various small doc fixes