Gather the config in a single file

Nb: After renumeroting the numbered list in the README a few times, it seemed
wiser to choose the lazy way ("It’s important to note that the actual numbers
you use to mark the list have no effect on the HTML output Markdown produces")
No more need to override versionned files with custom config

Seems easy to do asynchronous file copy with node, but I haven't found an easy way
to do it synchronously
(source of this code: http://procbits.com/2011/11/15/synchronous-file-copy-in-node-js)
http:// is part of the config file

By default mustache escapes slashes, hence the need to override its escape method
Made the logo url configurable
Merge pull request #2 from gturri/centralizeConf

Centralize configuration