add 'cargo-deny' linting

[danieleades]

adds cargo deny

Given this repo's security and stability ambitions, i think cargo-deny is a good fit.

This is not ready to be merged- input needed from maintainers to agree a sensible configuration (cargo-deny is highly-configurable)

[codecov[bot]]

Codecov Report

Merging #57 (4a696cd) into main (0c85cb0) will increase coverage by 0.06%. The diff coverage is 93.33%.

@@            Coverage Diff             @@
##             main      #57      +/-   ##
==========================================
+ Coverage   83.77%   83.83%   +0.06%     
==========================================
  Files          18       18              
  Lines        2102     2116      +14     
==========================================
+ Hits         1761     1774      +13     
- Misses        341      342       +1     

Impacted Files	Coverage Δ
src/doc.rs	56.92% <0.00%> (-0.77%)	:arrow_down:
src/test.rs	92.48% <100.00%> (+0.88%)	:arrow_up:

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[davegarred]

Very nice addition!