TeamCity test reporter

[fatuhoku]

Author of the Cabal TeamCity Plugin here.

As noted in the Known Issues section of the README, it would be great to have some native TeamCity reporting support from test-framework.

This would allow any test-framework-enabled project to have its tests reported painlessly with TeamCity, much in the same way that teamcity-messages does this for Python unittests. There is even support for parallel test run flows.

This issue may require an abstraction for pluggable test reporters that can be enabled by the user through command line flags. e.g. cabal test --test-reporter=teamcity.

The test reporter would spit out test execution details in the format of
TeamCity Service Messages, which TeamCity then picks up and provides all sorts of lovely metrics for.