Added new samples, HelloScreen and HelloTriangle

[JessyDL]

This PR adds sorely missing examples. They will show best practices, and will ease readers into understanding the core architecture.

Additionally some minor bugs were fixed such as:

• psl::library had competing default constructors
• psl::library had issues when constructing without a backed physical library file
• transforming a path to the windows version would lead to a crash if the path was 0 sized.

Minor new features:

• cmake targets can now specify a sub-directory for where the binary goes