initial commit for NarrowLookupTable
NarrowLookupTable:forward 1D works (unit tested)
NarrowLookupTable:forward 2D works (unit tested)
NarrowLookupTable:accGradParameters works (unit tested)
NarrowLookupTable:[accUpdateGradParameters,type] work (unit tested)
NarrowLookupTable ascDelta=true  works (unit tested) + doc
merge
Merge pull request #15 from nicholas-leonard/skewedlookup

NarrowLookupTable