Support DOM attribute parsing at compile & runtime

This addresses issue where locally bound value isn't properly converted to
React-friendly DOM attribute value because it isn't parsed at runtime.

When formatting DOM attributes at compile time and we run into a symbol, call
the format function at runtime.

Fixes #33
Extend runtime format-opts to all non-literals

Call format-opts at runtime if value is any non-literal value, not just symbols.
Merge pull request #34 from Prismatic/recursive-format-opts

Support DOM attribute parsing at compile & runtime