system-source: A tool to expand system()

When system() was turned into a C module, it became harder to figure out
what it expands to. This patch adds a small and simple tool that will
create a temporary syslog-ng config file, and extract the part system()
expanded to. This fixes #94.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #134 from algernon/f/system-expander

system-source: A tool to expand system()
system-source: Include system-expand in the dist tarball

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
libtest: Install the library, headers and pkg-config file

This opens up the possibility of using the testing framework in external
modules, too.

Requested-by: Viktor Tusa <tusavik@gmail.com>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
type-hinting: Add support for double(...) type hints

This add support for double(...) type hints, to type-hinting only. None
of the drivers were updated to use it yet.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
mongodb: Add support for double() type hints

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
format-json: Add support for double() type hints

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>