Implement CUDA IProductWRTDerivBase sum-factorization kernels

See merge request !14

Add error message if both CUDA and SIMD are enabled.

See merge request !19

Fix tests missing main function

See merge request !21

Implement CUDA PhysDeriv sum-factorization kernels

See merge request !13

Implement CUDA IProductWRTBase sum-factorization kernels

See merge request !12

Fix memory leak with Field objects not being deleted.

See merge request !16

Fix merge error

Closes #4

See merge request !15

Implement CUDA BwdTrans sum-factorization kernels

See merge request !11

Add a `Field::compare` method

See merge request !9

Add IProductWRTBase operator and standard matrix implementation

See merge request !10

Fix/wrong expid for block

See merge request !5

Add unit test for BwdTrans operator

See merge request !4

remove unnecessary std::move from Operator ctors

See merge request !6

fix Field move assignment ctor

See merge request !7

Implements BwdTrans StdMat operator

See merge request !2

Updated code to use a common base class and single factory pattern.

See merge request !1

Expand on the comments in main.cpp.