Add feature list support to DroidDoc.

Similarly to intent actions/categories, DroidDoc look
for the FEATURE-type SdkConstant annotation and builds
a list of optional features for the platform.

This is then packaged with the SDK to be used by the
custom editors (manifest editor in this case)

Change-Id: Icb5cf14ebd8251017cd850eacfdbb889219b3697
1 file changed