Add getVar and getPar functions with arguments Variable or Parameter, respectively.

Properly make const those functions and arguments that need to be const.
Add Flatte resonance.
Add evaluate functions with new signatures, taking 2 or 3 real numbers
    for the Dalitz variables.
Add a function to evaluate a Funcion object given a map of variable names and values.
Add some frequently used functions related to the phase space.
Make Dataset getters throw a DataException if the requested column is not
     found in the dataset.
Add the possibility to push a map of data fields and values at once,
    instead of having to push every column individually.
Make Resonance getters return a const.
Make the evaluateFuncs method const.
Improve the generation in Decay3Body.
Simplify a little bit the cache function in Decay3Body.
Make getters return const and by reference, and add new getters for Dalitz variable names.
Get rid of unimplemented convolution operator.
Add functions to evaluate projections of pdfs over 1 or 2 variables.

Add class Region to set region limits in variables, which affects the pdf
    normalization and, therefore, the projections.