version 2.0

Changes:
1- handling lambda with any number of arguments (thanks to @KnairdA)
2- boost optional support (thanks to @Killili)
3- prepared statements (thanks to @Killili)
4- shared db connection (thanks to @Killili)
5- automated project tests with drone.io (thanks to @edrosten)
6- extracting data to std::touple (thanks to @edrosten)
7- better exception handling (thanks to @edrosten)

Many thanks to all great contributors of the project ;)