v0.3.10 - Performance improvements

Instrumentation and optimization.

New Features

• A new REGOCPP_ACTION_METRICS option is available. When turned on, it will compile rego-cpp with
  instrumentation to measure the number of times a Trieste action is executed and how long is spent
  in each.
• A new internal join method.

Improvements

• ValueDef now caches its str and json representations instead of computing them each time.
  This has had a significant impact on unification (~5x speedup)
• Use of the new join method reduces allocations and copies for common string operations
• The unifier can now act over Object, Set, and Array nodes directly.
• The functions pass has been refactored to produce fewer temporary variables and to perform
  fewer rewrites, reducing its runtime by half.
• The local variable fixing that used to happen in implicit_enums now happens in its own pass, enum_locals.