Rework the vulkan module:
- adopt the VULKAN_SDK paths for its linux version
- add sanity tests for the VULKAN_SDK path
- add guessing as last fallback, needed on linux systems
on which no vulkan pkgconfig is installed [ubuntu atm]
- restructure exception handling/branching
Not tested on windows yet.
This was broken because the class property will say True but the
object property will not be set. Store the value on the class property
and transfer to object in __init__. Just like PkgConfigDependency.
This class now consolidates a lot of the logic that each external
dependency was duplicating in its class definition.
All external dependencies now set:
* self.version
* self.compile_args and self.link_args
* self.is_found (if found)
* self.sources
* etc
And the abstract ExternalDependency class defines the methods that
will fetch those properties. Some classes still override that for
various reasons, but those should also be migrated to properties as
far as possible.
Next step is to consolidate and standardize the way in which we call
'configuration binaries' such as sdl2-config, llvm-config, pkg-config,
etc. Currently each class has to duplicate code involved with that
even though the format is very similar.
Currently only pkg-config supports multiple version requirements, and
some classes don't even properly check the version requirement. That
will also become easier now.
nyorain