Add $(LOCAL_PATH) when including files in the Android.mk

Since this Android.mk will be included by another one in a
different directory, the paths of the files have to be absolute.
Sync libevent
Point yaml-cpp to my personal fork of yaml-cpp

This repository containes some changes to make it work with
Android NDK.
Add yaml-cpp/include folder to the include path of Libight
Sync yaml-cpp with my repository
Sync yaml-cpp with my personal fork
Add boost headers to the Libight include path