Update libyaml to 0.1.6 for CVE-2014-2525

libyaml prior to 0.1.6 is vulnerable to a heap overflow which can lead to
denial of service or arbitrary code execution. This commit adds a knapfile for
libyaml 0.1.6, which can then be used to build ruby against.
Merge pull request #7 from haus/master

Update libyaml to 0.1.6 for CVE-2014-2525