Add groups to 2-D convolutions

[Rifur13]

Proposed changes

Added groups to 2-D convolutions for some kernel specializations.

Also fixed 1D grouped convs with different kernel strides and added more tests.

Can close out #100

Performance looks pretty good:

(N, H, W, C)	(O, kH, kW, C)	dtype	stride	pads	groups	diff%
(4, 64, 64, 256)	(256, 5, 5, 256)	float32	(1, 1)	(2, 2)	1	+25.78%
(4, 64, 64, 256)	(256, 5, 5, 256)	float32	(1, 1)	(2, 2)	2	+36.72%
(4, 64, 64, 256)	(256, 5, 5, 256)	float32	(1, 1)	(2, 2)	16	-23.80%
(4, 64, 64, 256)	(256, 5, 5, 256)	float32	(1, 1)	(2, 2)	64	+92.72%

Checklist

Put an x in the boxes that apply.

• [x] I have read the CONTRIBUTING document
• [x] I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have updated the necessary documentation (if needed)