I noticed a build failure for yaml-cpp (#328), that the boost
headers could not be found. Probably since the update to 0.5.2 [1],
yaml-cpp depends on boost. This commit resolves the issue by adding
this dependency.

[1] https://github.com/bmwcarit/meta-ros/commit/da10180fc561ba5da0271476f013d73b6733ea51



Signed-off-by: Lukas Bulwahn <lukas.bulwahn@oss.bmw-carit.de>

This commit adds the yaml-cpp recipe from the repository at
https://github.com/kartikmohta/meta-km. The file is licensed
with the MIT license
(cf. https://github.com/kartikmohta/meta-km/blob/master/LICENSE).

The original recipe can be found at
https://github.com/kartikmohta/meta-km/blob/master/recipes-devtools/yaml-cpp/yaml-cpp_0.3.0.bb

The README file acknowledges Kartik Mohta's contribution and names
him as a contributor.