Fixed step slicing and string indexing on NdMapping
Fixed step slicing and string indexing on NdMapping

mjabri/holoviews,basnijholt/holoviews,vascotenner/holoviews,ioam/holoviews,vascotenner/holoviews,vascotenner/holoviews,basnijholt/holoviews,mjabri/holoviews,basnijholt/holoviews,ioam/holoviews,ioam/holoviews,mjabri/holoviews