feat: Support for custom 'format' validators

[Stranger6667]

Resolves #158

[codecov]

Codecov Report

Merging #244 (3502ef4) into master (76cfe50) will decrease coverage by 0.19%.
The diff coverage is 58.33%.

@@            Coverage Diff             @@
##           master     #244      +/-   ##
==========================================
- Coverage   83.23%   83.04%   -0.20%     
==========================================
  Files          53       53              
  Lines        4056     4092      +36     
==========================================
+ Hits         3376     3398      +22     
- Misses        680      694      +14     

Impacted Files	Coverage Δ
jsonschema/src/keywords/format.rs	87.16% <39.13%> (-6.74%)	⬇️
jsonschema/src/compilation/options.rs	64.44% <92.30%> (+2.96%)	⬆️
jsonschema/src/error.rs	62.15% <0.00%> (+0.27%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 76cfe50...3502ef4. Read the comment docs.