Support to parse configuration files. By default, the default conf file
is parsed ({sysconfdir}/pinos/pinos.conf), but that can be changed with
an environment variable (PINOS_CONFIG_FILE). The file can contain
commands and assignments (no assignment supported this far).
Support for command module-load is added.
A module is a shared library existing in, or a subdirectory of, the
module directory. The directory is by default
${libdir}/pinos-$(MAJORMINOR)/modules, but can be specified with
--with-module-dir=PATH when running configure. It is also possible to
override the module directory runtime with the environment variable
PINOS_MODULE_DIR, which is a list of directories separated with ":".
It's possible that the last ref to a source-output is removed with
the remove signal, in that case, remove the object from the client
watched objects to avoid freeing it twice.
Use installed gstreamer and fix library name
