The last SCESets was been added multiple times
instead of adding each one onces.

Fixes #4

Make it clearer what is the package and what is the simulation

Validity method was set to SimpleParams

Not great, but will do for now

Zero means was causing NAs in counts

Some parameters weren't being passed from SCESet method to matrix
method

Getting note about scDatEx, but think it should be fine...

estimateSimpleParams -> simpleEstimate
estimateSplatParams -> splatEstimate

Neater than having a checkValid option

Make it clearer what is new and old