Properly implemenent handle statement

[JSAbrahams]

Relevant issues

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Summary

The handle statement now coincides with the grammar:

• It expects a newline before the conditions
• It does not require the when token after the handle token

Added Tests

Tests to verify

• That handle works correctly
• That raise works both in the function signature and in-line

Additional Context

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[codecov[bot]]

Codecov Report

Merging #82 into master will increase coverage by 0.84%. The diff coverage is 90%.

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
+ Coverage   80.52%   81.36%   +0.84%     
==========================================
  Files          60       61       +1     
  Lines        3974     3982       +8     
==========================================
+ Hits         3200     3240      +40     
+ Misses        774      742      -32

Impacted Files	Coverage Δ
src/lexer/token.rs	28.57% <0%> (ø)	:arrow_up:
src/parser/expr_or_stmt.rs	100% <100%> (+57.14%)	:arrow_up:
tests/parser/valid/error.rs	100% <100%> (ø)
src/parser/definition.rs	85.81% <0%> (+3.37%)	:arrow_up:
src/parser/_type.rs	87.68% <0%> (+7.97%)	:arrow_up:

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