Unlike the corresponding mktime C library function, the libdivecomputer
function will never modify its argument. By marking the parameter as
const this is made more explicit.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.