Log Message:
Update textproc/yaml-cpp to 0.5.3.

This will be the last release that uses Boost; futures releases
will require C++11 instead.

No release notes, only bugfixes since 0.5.1. See full commit logs:

https://github.com/jbeder/yaml-cpp/compare/release-0.5.1...release-0.5.2
https://github.com/jbeder/yaml-cpp/compare/release-0.5.2...release-0.5.3