Fix all but one broken test in core_test
Add `cssfn` and `defcssfn` for creating and defining CSS functions
Default :output-style flag is :compressed not :expanded
Several updates to compiler and core (Fixes #11)

Compiler updates:
  - Discard `with-output-syle` and prefer configuration with *flags*
  - Extend Expandable and Renderable to additional types
  - Use `render-value` instead of `to-str` for slightly more control

Core updates:
  - `css` is no longer a macro #11
  - Add new function `style` for inline HTML styles