Migration to data.table underway
Migration to data.table rather than dataframe under the hood.
Passes all regression tests.
There may be legacy code that will have to be changed.
todt() is for to data.table, and converts a character string from getMapping to an expression that can be evaled inside of the j-expression of data table to retreive a set of columns. Better than passing with=FALSE since it allows you to build up expressions for aggregation within data.table
Migrate to data.table. Merge with master in regression branch.

Merge branch 'data.table' into regression

Conflicts:
	DESCRIPTION
	NAMESPACE
	R/AllClasses.R
	R/Fluidigm-methods.R
suppress messages and warnings from fread about parameters.
merge namespace