remove isDebug (BREAKING CHANGE for default) and add simple log

Removing bad idea of `isDebug`, see #822.

This means you must use `Ractive.defaults.debug` not `Ractive.debug`

For @ractivejs/team-ractive,  I rolled all the uses of debug into a `log` module along with associated messages (which are all in `config/errors`). Still need to move the straight `throw` cases to use this class. __Do not__ use `log` for instrumentation logging. It's only for non-golden path execution after a condition has been determined.