Raise an error on carriage return in multi-line basic string

[hukkin]

For context: toml-lang/toml#837 (comment)

[codecov-commenter]

Codecov Report

Merging #108 (8b8be54) into master (1b35b36) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #108   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          491       491           
  Branches        95        95           
=========================================
  Hits           491       491           

Impacted Files	Coverage Δ
tomli/_parser.py	100.00% <100.00%> (ø)

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