Fixed time delay in tests.

Since sleep() takes an int as argument, there was effectively no delay before, was caused the tests to fail on some machines.
Changed to yaml-cpp version 1.5.1

Version 1.5.0 introduced a new API, thus this is a breaking change. Also, the new yaml-cpp was built with a current Boost library, so upgrading the latter will also me necessary for most users.
Bugfixing for yaml-cpp 1.5.1 and removed comments.

Note that for this to work, also the old library files have to be removed. For a Mac, those are the files `/usr/local/lib/libyaml-cpp.*` prior to the installation of the new yaml-cpp version.
Updated Readme: Required yaml-cpp version.
Merge branch 'yaml-cpp-v0.5'

This closes issue #7, as dicussed there.