Fix openJdk package-level javadocs

Libcore was missing few 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 solves the

Bug: 29114138
Change-Id: Id16a645879ec7b34155a8d9d8ae6cd3b0b92b43b
11 files changed