Changed null pointer definition in common.h.

NULL is now (void *)0 in C and default in C++.
Function create_empty_bam_header only accepts unsigned int now (not
negative).

The parameter num_chrom is now unsigned int.
Function create_empty_bam_header return NULL if num_chroms is 0.
Added limits to probability calc in aux_math.

The limits are in recal_config.h
First testing implementation, with check.
Changed parameter size in aux_vector functions to unsigned int.
Merge branch 'testing' into develop
Fix: Added unsigned to size in initialize_vector function (aux_vector).
Aux_vector.c now checks if parameter size in functions is 0.
Implementation for aux_library_testing.
Removed "common.h" from timestats.h (not needed).
Added NULL error handling and warnings to timestats lib.
Added include directory to store public interface headers.
Added test case (not implemented) for timestats.c.
Added some test code to timestats.
Minor changes in timestats checking.
Fix: Configure now generates tests folder Makefiles.
Added 'make dist' support.
Fix headers of timestats.c
Changed timestats public pointer from (void *) to p_timestats.