Byfl v1.5 for LLVM/Clang v3.7.1

This is mostly a clean-up release of Byfl. The main user-visible change is that instrumented programs now produce far less textual output: only the BYFL_INFO and BYFL_SUMMARY lines. The intention is to reduce clutter. Most of the now-removed textual output was too wide to fit in any normal-sized window without wrapping. No changes have been made to the binary data an instrumented program writes to the .byfl file.

At configuration time, convenient new EXTRA_CPPFLAGS, EXTRA_CFLAGS, EXTRA_CXXFLAGS, and EXTRA_LDFLAGS variables enable users to append flags to those needed by the LLVM SDK.

The build-llvm-byfl script has been removed. It was too difficult to maintain, especially relative to its limited utility.