Update options.mk.sample

Added support for Lapack libraries (C interface) on GNU/Linux distributions.
Update lapack_wrap.h

Added support for Lapack on GNU/Linux systems by using LAPACKE header (C interface to Fortran Lapack)
Update utility.cc

Fixed error: expected unqualified-id before ‘__extension__’
 static Complex I(0.0,1.0), C1(1.0,0.0),C0(0.0,0.0);
                ^
utility.cc:453:16: error: expected ‘)’ before ‘__extension__’
with PLATFORM=lapack
Merge pull request #56 from jalfonsi/patch-3

Update utility.cc
Merge pull request #55 from jalfonsi/patch-2

Update lapack_wrap.h
Merge pull request #54 from jalfonsi/patch-1

Update options.mk.sample
Allowing S- and S+ in addition to Sp and Sm in spin Models. Added S2 (S squared) operator to both.
Updated ExtendedHubbard.h to use new Model interface and changed design of kinetic energy part.
Updated sample/exthubbard to use latest InitState/Model interface.
Added back named operator methods to Hubbard Model class for backwards compatibility
Added feature allowing operator strings of the form Op1*Op2, telling Model objects to return the product of Op1 and Op2.

Fixed conflicts:
	itensor/model.h
Updated exthubbard sample code and input file to use latest library interface.
Added back older Model class interface to SpinHalf, SpinOne, Spinless, and tJ models for backwards compatibility.
Moved recently added endif to just below initial ifdef I