* isValidUtf8 function, tests

* Cleanup, change to forAll

* Fix accidentally-correct generation of wrong test cases

* Increase test count, fix segfault on Clang

* Try fixing Windows

* Eliminate block-checking for ASCII in fallback mode

* Use GHC 8.10 for CI on Windows

* Namespace externally-visible C function better

* Link to libgcc on Windows

* Fix error accumulation in AVX2 check

* Fix use of <> on older GHCs

* Repair Drone config to deal with older Cabal

* Ensure non-SSE2 x86 can still build

* License information and contact for C code

* Fix test name typo, allow more than pre-set count of tests

* Stop using MagicHash for FFI wrapper

* Revert change to 8.10 for Windows CI

* Use existing license verbatim for C code

* Explain the use of gcc and gcc_s

* More concise implementation of isValidUtf8

* Document AVX2 block-checking function