* Improve robustness of sample apps. Fixing crash in aviplay
* Changes in documentation
* Add first pjsua2 hello world sample (from PJSUA2 guide)
* Fix doxygen documentation for docs.pjsip.org v2
* Add make clean-doc target
* Replace Trac ticket URL with GitHub issues URL
* Remove pjsip-book because the correct one is in pjproject_docs