Features:
    o handle missing data in target matrix
    o NMF model/algorithm class for MCMC based NMF
    o function/option to run standard consensus clustering, 
    i.e. with a different set sample for each run. 
    Possibly also use subsets of features and consensus matrix for them (memory issue).
    o incorporate silhouette values/plots, notably in heatmaps
    o support for other type of matrix-like objects (e.g., bigmatrix, Matrix)
    o import/export functions

Documentation:
    o improve/update vignettes
    
Technical/Internals:
    o change plot.NMFrankestimate to screeplot, remove class NMFrankestimate, 
    change it to normal NMFlist
    o Switch to the interface defined in the package modeltools
    