Specify multiple label streams with the HTKMLFReader

The HTKMLFReader (the reader to read Master Label Files (MLF) of the Hidden Markov Toolkit (HTK)) can be configured to read multiple label streams. The example below is taken from TIMIT_TrainMultiTask_ndl_deprecated.cntk in the Examples directory:

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"
    }
}