Proposal for 2.3.0

[henryiii]

I'd like to recommend or make a few changes and release a new 2.3.0 version of GooFit in 2-3 weeks. These are the things I'd like to do that warrant the larger version bump:

• Drop support for older CMake. This is a common source of bugs, a huge maintenance burden and not hard for users to install. Drop support for CMake < 3.9 (< 3.12 even better) #106
• Drop support for CUDA < 8.0. 8.0 is already rather old.
• Drop (explicit?) support for arch 2.0. We should require 3.0 or 3.5, I believe (newer versions of CUDA drop support for older arches too, I think)
• Make a strong effort to support CUDA 9.2-10.2 (the current versions of CUDA). 8.0 is getting too old to be our most recommended version.
• Include any patches needed for the WIP Conda-forge version. GooFit package conda-forge/staged-recipes#10654 (Done in 2.2.3)
• Work on compile speed, support UNITY builds and maybe PCH.

And, mostly done:

• Better support for Python installs (proper PEP 517 CMake usage, for example)
• Fixes for some common build issues

[henryiii]

Note: A few more old-CUDA workarounds are left over:

GooFit/python/CMakeLists.txt

Lines 71 to 73 in d877226

	if(GOOFIT_DEVICE STREQUAL CUDA AND NOT NEW_CUDA)
	target_include_directories(_goofit PUBLIC ${CUDA_INCLUDE_DIRS})
	endif()