fix: remove wildcard (*) dependency constraint for crate publishing

[qartik]

Also sanitizes the READMEs a bit.

The last attempt to publish a crate using release PR #98 failed with:

error: failed to publish to registry at https://crates.io/
    
    Caused by:
      the remote server responded with an error (status 400 Bad Request): wildcard (`*`) dependency constraints are not allowed on crates.io. Crate with this problem: `serde` See https://doc.rust-lang.org/cargo/faq.html#can-libraries-use--as-a-version-for-their-dependencies for more information

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.54%. Comparing base (1fdc898) to head (549b554).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #105   +/-   ##
=======================================
  Coverage   83.54%   83.54%           
=======================================
  Files          26       26           
  Lines        4016     4016           
  Branches     4016     4016           
=======================================
  Hits         3355     3355           
  Misses        343      343           
  Partials      318      318           

Flag	Coverage Δ
rust	83.54% <ø> (ø)

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[doug-q]

Thanks!