Gitignore gems and tmp directory.
Make the documentation formatter concurrent.

The start of a spec is immediately reported if no other have started yet. The
rest of the details are pushed on a reporting stack and reported in the order
of finishing.
Test concurrent documentation reporting.

The documentation reporting should support concurrent test running.
Unfortunately this is hard to test without inspecting the output. By
running it as a separate task on Travis, we'll probably notice when
things go wrong.
Explain about Peck flavors.
Change the runtime color for slow specs.

In the documentation notifier we show the runtime for a specs. This adds
a color to this time when it runs longer than the configured cutoff.
Bump version to 0.3.0.
Merge branch 'features/documentation'