Threadsafe tcv_t - interface cleanup

Implemented locking for thread safe tcv_t
creation and initialization of tcv_t split.

Public funcitons in tcv.h use pthread_mutex to protect tcv_t
from data-race on tcv_t.data and tcv_t.functions

libtcv/tcv.h contains public client functions, all internal functions
and data types are hidden in tcv_internal.h

Fixed typos, implemented some more tests.

Signed-off-by: Thomas Ruschival <thomas@ruschival.de>
Fixed profiling/coverage options in cmake