generalize drcachesim to support arbitrary trace analysis tools

We plan to generalize drcachesim to support two types of trace analysis tools:

1. Tools that are cache-agnostic, will not interact with the cache or TLB simulator, and will operate on the memory stream in the trace on their own. These will simply use the tracer and the trace reader but not the simulator.
2. Tools built on top of the cache or TLB simulator that will analyze additional aspects of the trace in relation to cache misses and other simulator features. For these, the simulator will become a platform that may provide an event API.