Implement a differentiation options struct, replacing the flags.
Remove redundant member.
Annotate our special function for better certainty it is actually ours.
Add an example functor objects
Remove old-dated comment.
Simplify the diff signature.
Pass in the order of the derivative as compile time constant.
Cleanup useless code.
Function -> CladFunction.
Add more accurate comment.
Merge branch 'master' of https://github.com/vgvassilev/clad

Conflicts:
	tools/ClangPlugin.cpp
Implement handier interface.
Start working on user-oriented demos.
Improve clad's user interfaces.

Conflicts:
	test/FirstDerivative/ClassMethodCall.C
	test/FirstDerivative/StructMethodCall.C
	tools/ClangPlugin.cpp
Forward declare correctly the used function.
No need of -verify when there are no expected diagnostics.
Don't use the operator new (it needs #include-ion of extra header files).
Update the list of contributors.
Sort list alphabetically as we promise at the top.
Fix a typo.