Add microbit-pxt-code-extractor (disclaimer: a tool I wrote)

[maehw]

Resource description

I've added microbit-pxt-code-extractor.
It basically allows to "unzip" the contents (embedded source code and other files) of a HEX file generated by by the PXT-based Microsoft MakeCode IDE for micro:bit (web IDE).
Details can be found in the project's READM: https://github.com/maehw/microbit-pxt-code-extractor

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