The old files were scattered in several directories,
with an unusual name, but dependencies to the usual name,
and relative paths.

The new files are regrouped in a singled directory
(doc/examples/pc-uninstalled) with their usual name
and more absolute paths.

With this change, it becomes possible to compile the examples
with the ffmpeg build tree by setting the environment variable:
PKG_CONFIG_PATH=pc-uninstalled