Added debug options to Makefile, improvements on matrixfromoctopus.f90,
and change to allow for unrestricted matrices V (previously, only
purely imaginary matrices were allowed).
Added the file tdfield_m.f90.

This file will contain everything about the td fields. Correspondingly,
I had to include it in the Makefile.
Added *.o and *~ to .gitignore.
Added initializations and finalization routines to tdfield_m.
Moved reference_tdfield and read_tdfield to tdfield_m

And added the routines tdfield_reference and tdfield_read, that
will substitute the previous ones, operating on the derived
data type tdfield_t.
Propagated the tdfield_t into a couple of routines.
Added tdfield_get and tdfield_set.

This allows to start removing some of the previous "tdfield" variables.