Add support to the llvm-cov show command for creating html reports.
This adds a new SourceCoverageView and a new CoveragePrinter specialized for emitting html. I modified two existing tests used for validating textual reports to validate the html.
I used an instrumented llvm-as tool to assemble test/Bitcode/compatibility.ll, and generated a coverage report based on the results. You can get the report here: bitcode-compatibility-coverage.dir.tar.gz.
Based on a patch by Harlan Haskins!