* fixes for Go 1.13 + retain go module 1.12 GOPATH behavior for internal/examples
* update docker images to 5.13.0
* new docker images (windows_64_shared_512, linux_512, darwin_512)
* update examples to match the Qt 5.13 api
* bump android minSdkVersion to 21 (5.0 / lollipop)
* bump OpenSSL version for android docker deployments to 1.1.1a
* let the binding use the 513 env by default
you can use QT_VERSION=5.12.0 and/or QT_API=5.12.0 to keep the binding backward compatible with your code
just setting QT_API=5.12.0 alone should also be sufficient to keep docker deployments working
if you did install an official Qt version then just set the correct QT_VERSION and procede as usual
* various minor fixes and cleanups
* support interface{} returns for js/wasm
* fix android builds on darwin
* support for the virtualkeyboard module
* fixes for docker image builds
* cleanup callback handling
* fix possible moc memory leaks
* new virtualkeyboard examples
1. the qt api changed in various places
2. dropped the "_minimal" suffix for the deployment folders
3. to keep using older versions of Qt (5.7.1 for example), one would
now need to explicit export "QT_VERSION=5.7.1" and also
"QT_DIR=/path/to/Qt5.7.1"
