Makes it apply to any version of boost from here on.

Signed-off-by: Khem Raj <raj.khem@gmail.com>

The ROS package cv_bridge needs the Boost.Python library. This
commit adds a bbappend file that includes Boost.Python in the
boost recipe using PACKAGECONFIG.
This PACKAGECONFIG for boost is available since commit
7568bfdd114597956a1da68746f207ec7f93a48d
in the openembeddded-core repository [1].

[1] http://cgit.openembedded.org/openembedded-core/commit/?id=7568bfdd114597956a1da68746f207ec7f93a48d

Instead of maintaining a copy of the tinyxml recipe from the meta-oe layer, we
require that the installation also includes the meta-oe layer.
We updated the README accordingly and also updated the description of the
current setup. We also updated and tuned the CONTENT file.

This commit resolves issue #45.

Replace CXXFLAGS += "-fPIC" with EXTRA_CXXFLAGS to allow native
build and use relative paths to simplify recipe.

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>