cufft.py module excluded from API docs

[yousefmoazzam]

In #494 the cufft.py module was intentionally excluded from the index.rst file:

httomo/docs/source/developers/api.rst

Lines 1 to 28 in 8a55c4d

	API
	===
	.. autosummary::
	:recursive:
	:toctree: generated
	httomo.base_block
	httomo.block_interfaces
	httomo.cli
	httomo.cli_utils
	httomo.darks_flats
	httomo.data
	httomo.globals
	httomo.loaders
	httomo.logger
	httomo.methods
	httomo.method_wrappers
	httomo.monitors
	httomo.preview
	httomo.runner
	httomo.sweep_runner
	httomo.transform_layer
	httomo.transform_loader_params
	httomo.types
	httomo.ui_layer
	httomo.utils
	httomo.yaml_checker

due to not knowing how to handle the error thrown when the CuFFT library isn't found:

httomo/httomo/cufft.py

Lines 29 to 41 in 8a55c4d

	# Load library
	_libcufft = None
	for _libcufft_libname in _libcufft_libname_list:
	try:
	_libcufft = ctypes.cdll.LoadLibrary(_libcufft_libname)
	except OSError:
	pass
	else:
	break
	# Print understandable error message when library cannot be found:
	if _libcufft is None:
	raise OSError("cufft library not found")

The cufft.py module is purely for memory estimation, and because the memory estimators will be moved from httomo to httomo-backends (see #429), this issue will likely become irrelevant to httomo and instead become relevant to httomo-backends.