[LLVM-C] Begin to Expose A More General Binary Interface

Summary:
Provides a new type, `LLVMBinaryRef`, and a binding to `llvm::object::createBinary` for more general interoperation with binary files than `LLVMObjectFileRef`.  It also provides the proper non-consuming API for input buffers and populates an out parameter for error handling if necessary - two things the previous API did not do.

In a follow-up, I'll define section and symbol iterators and begin to build upon the existing test infrastructure.

This patch is a first step towards deprecating that API and replacing it with something more robust.

Reviewers: deadalnix, whitequark

Reviewed By: whitequark

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60322

llvm-svn: 357822