Estimate per snp priors

```
per.snp.priors(
nsnps,
pa = 3.82e-05,
pc = 0.00182,
p1 = NULL,
p2 = NULL,
p12 = NULL
)
```

- nsnps
number of SNPs

- pa
prior probability that a non-query variant is causally associated with the query trait (cophescan prior), default 3.82e-5

- pc
prior probability that the query variant is causally associated with the query trait (cophescan prior), default 1.82e-3 (cophescan prior)

- p1
prior probability a SNP is associated with trait 1, (coloc prior), pc derived by using \(pc = p12/p1+p12\); use p1, p2, p12 only when pa and pc are unavailable (See vignettes)

- p2
prior probability a SNP is associated with trait 2, (coloc prior), pa derived by using \(pa = p2\)

- p12
prior probability a SNP is associated with both traits, (coloc prior), pc derived by using \(pc = p12/p1+p12\)

priors at the query variant