Add "cover" target to Makefile

This adds a new `cover` Make target to update and view test suite
coverage.
Add Makefile target to create SQLite DB

The `workbench.db` target is a prerequisite of the `install` target.
Merge pull request #26 from stvstnfrd/make/coverage

Add "cover" target to Makefile
Merge pull request #28 from stvstnfrd/make/db

Add Makefile target to create SQLite DB