Don't fail CI on coverage issues

Improve dead code elimination

Prefer putting tests in a `mod tests` section

Regenerate Cargo.lock to remove dependency on yanked 'quote 1.0.2'

Updated to LLVM 8.0.

Fixed a linking error on recent LLVM versions, and a pass manager
segfault on LLVM 8.

Updating changelog.

Prepare for v1.6.0 release.

Documenting building against LLVM 3.8.

Fixes #8.

Adding unit tests for compiling read and write instructions.

Add a screenshot of diagnostics.