ADAM variant and genotype formats; and a VCF->ADAM converter

Introducing a Variant format and a converter VCF --> ADAM. Takes in a VC...F as a text file. It can be gzipped (I think Spark is smart enough for that).

    The parsing is done manually. I attempted to adapt org.broad.tribble and org.broadinstitute.variant to help with a robust conversion; but the classes
    rely too heavily on a flat text file (can't set the header manually), and are not serializable (so can't be broadcast). The problem runs so deep that
    even with access to the source, I found it unworkable.

    Currently the schema are nested:

    ADAMVariant
     ... site-specific information ...
     array<ADAMGenotype>
           |
           | .. genotype-specific information ..

    however the info and format fields are rendered as strings rather than maps.