Version 0.15 of Lily.

Not only did this release last for 6 months (don't ask why), it's very
lackluster. Most of the information can be found in the RELEASES.md
that was added in the commit that this was tagged with. As such, this
will be a shorter version of that.

* string::split, and subscriptable strings. Oh boy, you can actually
  do things now!

* I made a Tainted class that represents evil things. You have to pass
  a sanitizing function to get the data inside. Apache provides post,
  get, and env as `hash[string, Tainted[string]]`. This is a step
  toward making SQL/XSS injection harder.

* I borrowed F#'s `|>` added. I like this.

* Exception traceback is now `list[string]` so that you can use string
  functions on it instead of changing it into a string and using
  string functions on it.

* I sprinkled some of Ruby's ideas on the list and hash classes until
  the shaker was almost empty.

* Function inputs are contravariant, and the output is covariant. All
  other things are invariant. Variance is really hard so I'm not
  letting other users do that right now.

* The mod_lily bridge provides some simple html printing functions.
  However, print still writes to html in server mode, so it's kind of
  silly.
  In a future release, I'll take that ability out.
