Adds an annotation-based profiling API for measuring the performance of Hatchet and Thicket

[ilumsden]

This PR adds APIs that can be used to measure Hatchet and Thicket's performance. By default, these APIs will do nothing. However, users can set the HATCHET_PERF_PLUGIN environment variable to enable these profiling APIs with a specified profiling tool. Currently, the following values for HATCHET_PERF_PLUGIN are recognized:

• caliper: use the Caliper Python bindings from LLNL/Caliper#573
• perfflowaspect: use PerfFlow Aspect
• none: disable profiling APIs. This is what is used when the environment variable is not set

These values for HATCHET_PERF_PLUGIN are case-insensitive.