initial commit for the elm logger

A basic implementation of ELM, a wannabe ELMAH. Currently the logs are written to a dictionary and are displayed in plain text

![elmloggerinitial](https://cloud.githubusercontent.com/assets/2818455/4650805/c8578f66-5496-11e4-9e85-dc8d51da1d1a.png)

You should directly compare the `PathString` instances instead of their `Value` property.

I'd also recommend setting `/Elm` as a default value either in the constructor or directly in `ElmOptions` (like the security middleware)