moved couplet.h to include/libcouplet/

This is new location of libcouplet API.
cleanup bootstrap.sh
fixed include couplet.h
revert 5e1fc51502239472f10299ae4ed4c3be5ce578a3

Abstracted XML parser API moved to src/parser.h
distinguish public API includes
fixed timeout calculation in xmpp_sem_timedwait
added xmpp_sem_timedwait to thread API
added semaphore for the event loop control

Added event_loop_sem to ctx_t structure. It's initialized as locked and
event loop runs until it becomes unlocked. The semaphore must be
increased by the number of threads.