`--random` requires an argument

[plavin]

It should pick a random seed if one is not provided

[jyoung3131]

Let's also standardize on using PCG and remove the Mersenne Twister RNG. it looks like it is only used in sgbuf.c.

line 43: for(size_t i = 0; i < len-2; i++){
//Need to replace this with equivalent PCG line
size_t j = (genrand64_int64() % (len-i)) + i;
for(size_t k = 0; k < worksets; k++) {