Restructure crate features

[ureeves]

Describe what you want implemented The features of a crate should be named accordingly to the features they enable, and not the names or technicalities of its dependencies. I propose a restructuring of the features of this crate.

Describe "Why" this is needed Currently the features included with this crate are:

default
alloc
rkyv-impl

Almost the entire crate sits behind the alloc feature with following exceptions:

cipher::PoseidonCipher                                                                                   
perm_uses::two_outputs                                                                                   
sponge::hash                                                                                             
sponge::truncated::hash 

I propose that this is terribly confusing, and as such we should rethink the features of the crate.