move code into src/ subdirectory
Revert "fix flags in documentation"

This reverts commit 062f5aea003211c32d562c7e5658ddd48825cb4a.
simply *and* harden str_to_int

Less code to boot :)
use for instead of while loop in str_to_num
start collecting global state

Stating with 'regex_t *re', move it into a structure which we'll pass
round shoot.c to avoid globals.
Move addrinfo into shoot_t
Remove fqdn from the set of globals
Don't have a global cseq_sequence.

Currently stashed with the other globals in shoot_t, but sipsak's state
and the connection's state should probably end up seperated.
simplify str_alloc, eventually kill it
use dbg in more places, add format attribute
drop swap_buffers; dead code
move swap_ptr to shoot.c