Fix openJdk package-level javadocs
Libcore was missing few package-info.java/package.html files
for few packages, I've added the relevant files from openJdk 7u40.
In 3 packages (java.nio, java.nio.charser, java.lang.ref) the
package.html file was not being included in the generated documentation
for unknown reasons. Still investigating the cause, but in the meantime
I did found that converting package.html into package-info.java solves the
11 files changed