Create readers for synthetic workloads

[1a1a11a]

Currently libCacheSim provides Python scripts to generate synthetic workloads, e.g., Zipf. However, this requires two steps: generating a Zipf trace and loading it into caches.
We would like to create a few trace readers that generate synthetic traces on the fly, e.g., uniform, Zipf. We expect the following usage

./cachesim Zipf_n_m_x.y syn  

where n is the number of requests, m is the number of objects, and x.y is the skewness.