Android is deprecating ndk.dir in favor of specifying exact NDK
version in Gradle configuration. Ensure that we can support multiple
NDKs, and link them into the location the Android Gradle Plugin expects.
androidenv did not previously write license files, which caused certain
gradle-based Android tools to fail. Restructure androidenv's list of
Android packages into a single repo.json file to prevent duplication
and enable us to extract the EULA texts, which we then hash with
builtins.hashString to produce the license files that Android gradle
tools look for.
Remove includeDocs and lldbVersions, as these have been removed
from the Android package repositories.
Improve documentation and examples.
I used the existing anchors generated by Docbook, so the anchor part
should be a no-op. This could be useful depending on the
infrastructure we choose to use, and it is better to be explicit than
rely on Docbook's id generating algorithms.
I got rid of the metadata segments of the Markdown files, because they
are outdated, inaccurate, and could make people less willing to change
them without speaking with the author.
This system type was previously broken but is now fixed.
Add it here to showcase the common task of launching a fully-fledged Android
system with an included app store.
