Log of breaking changes in 0.2 beta

[jbloom]

see:

[Breaking Change] sample_qc

The following changes have been made to sample_qc: The fields gq_mean and gq_stdev have been replaced with gq_stats that is a struct with four fields: mean, stdev, min, and max. The fields dp_mean and dp_stdev have been replaced with dp_stats that is a struct with four fields: mean, stdev, min, and max. n_singleton now includes singleton alleles that are the reference allele.