Update documentation

- The list of examples was not showing in the index page.
- Added information about types, method signatures, J2N and GC.
- Fixed some typos.

Change-Id: Ibe66ddbc0b1cac323563d629ca82bfe54d69dfc1
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>