core: provide ps argument

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: add glib extension/helper functions

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: construct full perf exec string

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>