This makes use of proper ConfigTool and PkgConfig dependencies rather
than one big ExternalDependency that internally creates other
dependencies and then copies their attributes.
Currently PkgConfig takes language as a keyword parameter in position 3,
while the others take it as positional in position 2. Because most
dependencies don't actually set a language (they use C style linking),
using a positional argument makes more sense. ExtraFrameworkDependencies
is even more different, and duplicates some arguments from the base
ExternalDependency class.
For later changes I'm planning to make having all of the dependencies
use the same signature is really, really helpful.
Dylan Baker
Daniel Mensinger
Michael Hirsch, Ph.D