use int instead of bool for C function rt_unloadLibrary

- This should actually be ABI compatible but it's cleaner
  for documentation purpose.
Merge pull request #623 from dawgfoto/rt_loadLibrary

use int instead of bool for C function rt_unloadLibrary
Add declaration of CP_UTF8
Merge pull request #637 from JakobOvrum/cputf8

Add declaration of CP_UTF8
made windows stack traces 10 times faster
Merge pull request #638 from Ingrater/fastTrace

made windows stack traces 10 times faster
remove unnecessary try/catch block in nothrow method
refactor Duration._toStringImpl to reduce code and object size
Merge pull request #640 from dawgfoto/refactorDurationToStringImpl

refactor Duration._toStringImpl to reduce code and object size
use Throwable.toString to report unhandled exceptions

- Add toString(sink) overload to Throwable, so that
  it can be used without the GC.

- Rewrite string toString() in terms of the sink overload.
  Thus toString(sink) becomes the preferred method to
  override in derived Throwables.
kill console