Add Exception instance for TOMLError

[tbidne]

Resolves #13.

Hi! First, thanks for the great library. The API is excellent.

I am happy to discover this issue, as I thought of the same thing when using it :slightly_smiling_face:.

[codecov-commenter]

Codecov Report

Merging #15 (d44448c) into main (86b0e2c) will decrease coverage by 0.08%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
- Coverage   57.72%   57.63%   -0.09%     
==========================================
  Files           6        6              
  Lines         693      694       +1     
  Branches       19       19              
==========================================
  Hits          400      400              
- Misses        287      288       +1     
  Partials        6        6              

Impacted Files	Coverage Δ
src/TOML/Error.hs	81.81% <0.00%> (-1.91%)	:arrow_down:

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[brandonchinn178]

Thanks!

[tbidne]

Thanks for merging!