Log Message:
Update to 0.4.2.3

CHANGELOG:
0.4.2.3
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 * It builds against 7.4.2 (not 7.4.1), so update the constraints.

0.4.2.2
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 * Builds with ghc 7.10
 * Builds again with ghc 7.4
 * Drops dependency on utf8-string

0.4.2.1
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 * Better error reporting (thanks to Corentin Dupont)