add metrics for ExecutorService and ThreadFactory
'wrappee' sounds silly, renaming
add javadocs for java.util.concurrent instrumentations
implement ExecutionService instead of inheriting from AbstractExecutionService
rename underlying implementations as 'delegate'
use MetricRegistry#name instead of doing concatenation manually
use a Meter for completed tasks
make Metric members private and retrieve them from the registry for testing
format to adhere to project code convention
mark fields as final, removed a stdout statement
use meters for 'created' and 'finished'/'terminated' metrics
have both test classes terminate the generated threads cleanly
Merge pull request #411 from fernandezpablo85/master

instrumentation for java.util.concurrent classes