rename Uniform -> Rejection

[mileslucas]

I wanted to rename Uniform -> Rejection in the Proposals module because I think it is a better name. Despite this repo being pre-v1.0, I'll deprecate the Uniform constructor since I'm making a superficial change.

[codecov]

Codecov Report

Merging #71 (bee2568) into main (6b09bb7) will not change coverage.
The diff coverage is 100.00%.

❗ Current head bee2568 differs from pull request most recent head b965e1b. Consider uploading reports for the commit b965e1b to get more accurate results

@@           Coverage Diff           @@
##             main      #71   +/-   ##
=======================================
  Coverage   90.39%   90.39%           
=======================================
  Files          12       12           
  Lines         531      531           
=======================================
  Hits          480      480           
  Misses         51       51           

Impacted Files	Coverage Δ
src/proposals/Proposals.jl	93.29% <100.00%> (ø)
src/staticsampler.jl	100.00% <100.00%> (ø)
src/step.jl	94.35% <100.00%> (ø)

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