Download executor JAR file with all dependencies

This small library provides an optimized solution to a problem where tasks for a particular key need to be processed sequentially as they arrive. This kind of problem can be solved by a SingleThreadExecutor, however it is not efficient. The issue is that the tasks for unrelated keys are not being processed in parallel, instead they are put into a queue common to all keys and wait for the single thread to execute them. This library allows them to be executed concurrently. Moreover this library works well in a situation where all the possible keys and their number is not known upfront.