Merge pull request #143 from unittest-cpp/v2-prep

v2.0.0 prep

Closes #96

Merge pull request #111 from unittest-cpp/v1.6.1-prep

v1.6.1 prep

Update docs, versions for 1.6.0.

Prepare v1.5.1 tag

Prepare v1.5.0 tag.

Tagging v1.4 as previously released on sourceforge.