adam beta2 to 0.99, as recommended by variational ddpm paper, and dal…

…le2 training has been good with it

oops not ready yet

been using the same ema logic across a number of my repos now, time t…

…o move it out and maintain it

do softmax in float32

allow for conditioning on an image of any number of channels, for @de…

…epglug pose conditioning problem

0.7.7

scaffold for eventual "imagen <text>" command line tool

allow for removing final resnet block

add ability to configure final conv kernel size

allow for fine specification of whether unet in cascade should use dy…

…namic thresholding