added option to disable writing to emulated tag and fixed ndef size information

Signed-off-by: Armin Wieser <armin.wieser@gmail.com>
Merge branch 'master' of github.com:Seeed-Studio/PN532
enabled debugging

Signed-off-by: Armin Wieser <armin.wieser@gmail.com>
Merge pull request #8 from awieser/master

fixed: ndef size + possibility to set emulated tag read only