sample int-sorting framework using qsort
go C99 for declaring variable length array
implement sleep_sort using posix threading
add random_sort
use the same input array for all sorts
sleep sort now can deal with negative inputs
separate out int value from sleep_time
add random_sleep_sort
replace conditional logic with function pointer
replace magic number with enum and else-if with switch
add timing info to output
move mutex to heap
remove un-needed function declaration in public header
move #define _GNU_SOURCE from public header to .c file
clarify function pointer
make names more consistent
remove blank line
make -std=c89 for improved portability
replace constants as defaults for commandline options