CompilerGym v0.1.6

This release focuses on hardening the LLVM environments, providing improved
semantics validation, and improving the datasets. Many thanks to @JD-at-work,
@bwasti, and @mostafaelhoushi for code contributions.

• [llvm] Added a new cBench-v1 dataset which changes the function attributes
  of the IR to permit inlining. cBench-v0 is deprecated and will be removed no
  earlier than v0.1.6.
• [llvm] Removed 15 passes from the LLVM action space: -bounds-checking,
  -chr, -extract-blocks, -gvn-sink, -loop-extract-single,
  -loop-extract, -objc-arc-apelim, -objc-arc-contract, -objc-arc-expand,
  -objc-arc, -place-safepoints, -rewrite-symbols,
  -strip-dead-debug-info, -strip-nonlinetable-debuginfo, -structurizecfg.
  Passes are removed if they are: irrelevant (e.g. used only debugging), if they
  change the program semantics (e.g. inserting runtimes bound checking), or if
  they have been found to have nondeterministic behavior between runs.
• Extended env.step() so that it can take a list of actions that are all
  performed in a single batch. This improve efficiency.
• Added default reward spaces for CompilerEnv that are derived from scalar
  observations (thanks @bwasti!)
• Added a new Q learning example (thanks @JD-at-work!).
• Deprecation: The next release v0.1.7 will introduce a new datasets API that
  is easier to use and more flexible. In preparation for this, the Dataset
  class has been renamed to LegacyDataset, the following dataset operations
  have been marked deprecated: activate(), deactivate(), and delete(). The
  GetBenchmarks() RPC interface method has also been marked deprecated..
• [llvm] Improved semantics validation using LLVM's memory, thread, address, and
  undefined behavior sanitizers.
• Numerous bug fixes and improvements.