Rename "num_kfrags" to "shares"

[fjarri]

Following the standard terminology in nucypher

[jMyles]

What's the story here? We don't like overhead?

[codecov-commenter]

Codecov Report

Merging #69 (fd691e2) into master (3d3adf3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #69   +/-   ##
=======================================
  Coverage   82.36%   82.36%           
=======================================
  Files          14       14           
  Lines        1083     1083           
=======================================
  Hits          892      892           
  Misses        191      191           

Impacted Files	Coverage Δ
umbral-pre/src/pre.rs	93.75% <100.00%> (ø)

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[fjarri]

This just brings the API in sync with the terminology already used in nucypher.

I do like overhead (and #48 is still open), but as I remember from Discord discussions, some people were against it. @derekpierre , for example.

Edit: wasn't Discord, but rather a github comment

[fjarri]

Merging this to keep API synced with the current nucypher terminology. #48 remains open.