Custom msg support

[jawoznia]

close #157

[codecov]

Codecov Report

Merging #179 (0fbb83b) into main (32e783a) will increase coverage by 0.32%.
The diff coverage is 76.69%.

❗ Current head 0fbb83b differs from pull request most recent head 2552d5f. Consider uploading reports for the commit 2552d5f to get more accurate results

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
+ Coverage   76.32%   76.64%   +0.32%     
==========================================
  Files          22       22              
  Lines        1098     1126      +28     
==========================================
+ Hits          838      863      +25     
- Misses        260      263       +3     

Impacted Files	Coverage Δ
sylvia-derive/src/message.rs	74.48% <59.37%> (-1.83%)	⬇️
sylvia-derive/src/multitest.rs	76.56% <70.00%> (+1.82%)	⬆️
sylvia-derive/src/parser.rs	81.57% <75.00%> (+0.77%)	⬆️
sylvia-derive/src/input.rs	81.57% <82.35%> (-3.36%)	⬇️
sylvia-derive/src/lib.rs	73.91% <100.00%> (-1.09%)	⬇️
sylvia-derive/src/strip_input.rs	91.42% <100.00%> (+1.10%)	⬆️
sylvia/tests/custom_msg.rs	100.00% <100.00%> (+75.00%)	⬆️

... and 3 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[hashedone]

LGTM