Adding ADAMFeatureField for projections over ADAMFeature.

For some reason, we'd neglected to include an ADAMFeatureField class in the adam.projections
package!  This commit fixes that.
Use the scala.Console.out rather than System.out in PrintADAM

This seems to allow us to (in tests) redirect the output stream using the
Console.withOut command.
Added a failing test for Features2ADAM

Features2ADAM fails because it doesn't include an 'index' field in its
second command-line argument, and therefore Args4j can't parse the Features2ADAMArgs
object off a command line.
Added the missing 'index' argument to the Features2ADAMArgs class

Fixes the bug tested in the previous commit.