Introduce exometer metrics into 2.0
Standardizes the projects build tooling

    1) Adds tools.mk for common dialyzer, xref, doc, and test targets
    2) Modifies the Makefile to use the common targets in tools.mk --
removing local implementations
    3) Adds Exometer reporter dependency exclusions to the Makefile
Merge branch 'feuerlabs-exometer3' into feuerlabs-exometer4