Implement a PCP Instrumentation API in Rust

The primary goal of this project is to build a native PCP MMV instrumentation library in Rust with a high-level API that developers can use in their applications to report arbitrary metrics at runtime. Metrics will be written out in the Memory Mapped Values format v1/2, which can then be read by a Performance Metric Domain Agent. Sub-goals include building a Rust API and command line utility to dump metrics from an MMV file, and examples of embedding the MMV instrumentation library inside popular Rust projects (such as Iron and Hyper).