Garbage Collector Stack Size needs to be customizable

[LK-Simon]

The ThreadGarbageCollector is self-instantiating (by design and necessity) so we need to add a define to set the desired Stack Size for its Thread.

Define ESPRESSIO_THREAD_GARBAGE_COLLECTOR_STACK_SIZE if it doesn't exist with a default value of 2000.

[LK-Simon]

Completed in 257e997