Make markdown.js work with IE8

IE8's Array.prototype.splice requires 2nd argument to specify the
number of elements to be removed. Without that, nothing is removed.

If JS compressor (e.g., yui) compresses markdown.js,

  ... function Markdown(dialect) {

will become something like:

  ... function g(d) { ...

Then, Markdown.dialects.Gruber becomes g.dialects.Gruber.
But IE8 does not understand this. The fix is just remove
"Markdown" from after "function".
Merge pull request #68 from tatsuhiro-t/master

Make markdown.js work with IE8