Add various Player properties to property list

Fixes trello#42.
add npm package "memwatch"
Merge pull request #51 from yelworc/trello#42

add various Player properties to property list
use memwatch for memory/GC metrics

* add some memory usage and garbage collection metrics
* add memwatch to REPL scope (to be able to manually trigger GC)
Merge pull request #52 from yelworc/memwatch

use memwatch for memory/GC metrics