Release 1.5.12

- Refactored VCF conversion, split into separate VCF writer and bcftools wrapper scripts
- Extra methods in Fluidigm and Sequenom AssayResult classes to support VCF converter
- Refactor SQL in Infinium database wrapper
- Run iput with '-K' option to verify checksum
- Remove in_transaction from SQLite query to enable access to read-only files