Adding a D Programming Language Compiler Wrapper tool that runs and caches D programs. This is an alternative to the existing `rdmd` tool. It's a rewrite that leverages a new compiler feature that allows it to run the compiler once instead of having to run it twice like `rdmd` does. I decided to create a new tool rather than trying to support both older and new compilers in the same tool. It also introduces new features like "Source Compiler Directives" which allow D Language source files to contain compiler configuration such as import paths, environment variables, etc.
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