Rework --scripts handling to allow module loading

The --scripts argument should not point to the top-level Premake folder rather than its src/ folder; this allows the modules/ folder to also be referenced along that same path.

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branch : feature/use-scripts-arg-for-modules
Update BUILD.txt to reflect new behavior of --scripts option

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branch : feature/use-scripts-arg-for-modules
Convert --scripts argument to absolute path on startup

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branch : feature/use-scripts-arg-for-modules
Merge --script argument changes for modules