Specify multiple label streams with the HTKMLFReader

The HTKMLFReader can be configured to read multiple label streams. The example below is taken from [TrainMultiTask.cntk]

    reader=[
        readerType=HTKMLFReader
        ...
        labels=[
            mlfFile=$MlfDir$/TIMIT.train.align_cistate.mlf.cntk
            labelMappingFile=$MlfDir$/TIMIT.statelist
            labelDim=183
            labelType=Category
        ]
        regions=[
            mlfFile=$MlfDir$/TIMIT.train.align_dr.mlf.cntk
            labelDim=8
            labelType=Category
        ]
]