sketches palladium macro definitions

1) `macro foo = ...` instead of `def foo = macro ...`
2) Boxity is specified via signatures, not via context types:
   blackbox macros say `macro foo: T = ...`, whitebox macros say `macro foo <: T = ...`
3) Reflection API is cakeless. `import scala.reflect.core._` is all that it takes
4) Most of the functions of the API require a context, which is passed
   around implicitly, originating in macro defs