Upcoming support for new CAM methods

[frgfm]

TorchCAM is now mature enough to welcome new CAM methods 👍
This issue is meant to track upcoming additions on the next release!

A few things to consider:

• TorchCAM is not meant to support all available methods. This should focus on the ones providing SOTA performances (or perf milestones)
• the rightful contributors have to be credited: if a piece of code is borrowed from someone else's implementation, that should be indicated ("borrowed from", "inspired by", etc.)

Here is the list of envisioned CAM methods:

• PolyCAM (paper, implementation)
• EigenCAM (paper, implementation)
• LiftCAM (paper)

Suggestions are welcome 😄