Clean up Clippy and Rustdoc configuration.

[briansmith]

Address almost all the Clippy lints and remove their allows. Remove the briansmith.org rustdoc references.

[codecov]

Codecov Report

Merging #275 (d5e7d4b) into main (c81f92e) will not change coverage.
The diff coverage is 62.50%.

@@           Coverage Diff           @@
##             main     #275   +/-   ##
=======================================
  Coverage   50.62%   50.62%           
=======================================
  Files          18       18           
  Lines        3751     3751           
=======================================
  Hits         1899     1899           
  Misses       1852     1852           

Files Changed	Coverage Δ
src/end_entity.rs	35.61% <0.00%> (ø)
src/lib.rs	27.75% <ø> (ø)
src/name/verify.rs	4.11% <0.00%> (ø)
tests/dns_name_tests.rs	88.88% <ø> (ø)
src/name/dns_name.rs	69.48% <100.00%> (ø)
src/signed_data.rs	100.00% <100.00%> (ø)
src/verify_cert.rs	94.07% <100.00%> (ø)

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