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* Switch to cmake for build
* Hide symbols

With this change, `BUILD_TRANSDUCER=1 python setup.py build_ext` now sees `-D_GLIBCXX_USE_CXX11_ABI=` in the compilation command. (Note: sox is C-only so it is not relevant to sox build process)

See also:
 - https://github.com/pytorch/text/pull/931
 - https://stackoverflow.com/a/55406930

* Use cmake for third party

* Apply patch to libmad

* Update gitignore

* Update docker test image

* Use env var for switching SoX build and default to not

* Update README

* Fix packaging/CI script

* Clean up extension build mechanism and extension location

* Add back the switch to depend on external sox

* Remove print

* Fix