add carbon_conf_t * param to all parse() functions

Avoid all the conf_parse_*() functions to operate on global variable
conf to make them work on future reload mechanism.
add function conf_parse() to parse all files
change return type of launch_*_thread() functions

Change return type of launch_*_thread() functions to return a pointer
to a newly allocated carbon_thread_t.
new carbon_threads_t struct with global var

New global variables threads of type carbon_threads_t* which contains
pointers to all carbon_thread_t of the program.
add new function threads_wait_all_stopped()

To wait for all threads of the program to stop at the end of main().
add missing int parameter to signal handler
add pointer to self thread in param of workers

Thread workers now have in parameters a pointer to self
carbon_thread_t*. This is intended to be used by pause/resume functions
for configuration live reload.
new function thread_init()

This function aims to initialize all carbon_thread_t members. As of now
this structure is rather empty but it will be filled soon for the
purpose of threads pause/resume mechanism.
add threads pause/resume mechanism

With many new functions, new carbon_thread_t structure members and
functions calls in thread workers main loop.
SIHUP handler to reload configuration at runtime

New functions conf_reload(), conf_copy() and conf_free() have been
introduced for this purpose. These functions are called by a new SIGHUP
signal handler in main thread.

SIGHUP signal is now blocked by other sub-threads.
updated todolist in README file