WIP: modification of gdt lm implementation

To allow evaluation on user provided tables
WIP: better code separation
Handle correctly case of missing rows in lm input data
Use static linking for the GDT library

Enabled by default only on linux.
Add functions in lm fit object to predict values
Add norm2 method to matrix

To compute the sum of squares of a matrix.
Add fit summary function with R2 for gdt lm objects