Rewrite README.md

It’s now a blog-like text that explains what all this is about. Images
to come soon.
Remove example.ceylon symlink

It was broken, and doesn’t work on GitHub anyway.
Add pushdown automaton in Ceylon type system demo

Unfortunately, you have to specify the type arguments, so the compiler
can only verify that you’ve written a correct run of the automaton; it
can’t “run” the automaton by itself.
Demonstrate: Ceylon type system is Chomsky-2-complete

This removes the previous commit’s restriction of having to explicitly
specify the type arguments. The compiler wasn’t able to infer the
RestStak type argument, so we give the function a regular argument of
that type.

Using this technique, it should also be possible to construct a pushdown
automaton with two stacks – that is, a Turing machine. This means that
the Ceylon type system is (most likely) TURING COMPLETE (with the
restriction that you can’t make the typechecker loop, so the number of
steps is hard-coded by the number of function invocations you make).