Add --dbgwas option

[johnlees]

Add an option to provide output in the right format for DBGWAS, so that pyseer can be used as an alternative option in their step2 association.

This format is:

pattern p-value q-value weight wald_statistic
88136 3.00629e-24 8.5599297686e-19 0.9890817 18.9613580655415

[mgalardini]

Seems like a good idea! An alternative option could be to have a script that does the conversion, so pyseer doesn't need to change.

[johnlees]

Nice suggestion -- I think that would also be preferable as a I believe all the p-values are need to calculate the q-values