have Travis and Appveyor build official release packages

Previously official packages were built on developer machines. Now that we have Travis and Appveyor we should leverage it for a centralized, standardized official release process.

Complications include:

• Having Dr. Memory as a sub-package
• Having clean, simple path names

Xref package.cmake command lines at https://github.com/DynamoRIO/dynamorio/wiki/New-Release

For weekly builds (#1967 (closed)) I ended up having each build job create its own package, for efficiency of having all platforms have their own without separate jobs to invoke package.cmake. But, this splits i386 and x86_64, and makes packages that don't look like official packages. As part of making official packages we may want to change the weekly to use package.cmake too: since they are only weekly the extra jobs should be ok.