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*   Removed samples as registered executables in the cabal file, to reduce
    dependences to a bare minimum.  For convenience, build script now also
    compiles the samples into the local directory if *stack* is installed.

*   Added experimental (unsafe) combinators for working with GADTs with
    existential types, `withGADT`, to *Numeric.Backprop* module.

*   Fixed broken links in Changelog.