Programl

This release fixes a bug in which, for some LLVM IRs, the control edge position
values for instruction nodes with outdegree > 1 would be incorrectly set to 0.

This micro release relaxes the version requirements of the protobuf and grpcio
Python dependencies, and adds torch to the core dependencies.

This release adds a much simpler, flat Python API. The API comprises three
families of functions: graph *creation* ops, graph *transform* ops, and graph
*serialization* ops. Each function supports simple and efficient parallelization
through an `executor` parameter, and can be chained together.

This release also adds support for LLVM 6.0.0.

Move model definitions out of the `programl` package and provide a prebuilt
wheel for the Python package.

Initial release.