Property compiler to easily use eco with express

[mapmarkus]

I've added a property to eco so you can declare it as a express compiler like this:

express = require 'express'
eco = require 'eco'

app = express.createServer()

app.configure ->
  app.register '.eco', eco.compiler

Should solve issue #12

[aseemk]

(Just commenting so I can get notified of updates. Thanks!)

[sstephenson]

Thanks for the patch -- I decided to change the Eco API instead in 5d62cdd, so that eco.compile is compatible with what Express expects.