New exceptions architecture.

Hoa\Praspel\Exception is now an interface. The root exception is
Hoa\Praspel\Exception\Generic.
We have also added the “Praspel failure” exceptions and the
Hoa\Praspel\Exception\Group exception.
New RAC for Praspel: cleaner and faster.
[auto] Merge from Praspel

    • #deb81e7 — New exceptions architecture. (Ivan Enderlin, 2013-06-07)
    • #af0ab4b — New RAC for Praspel: cleaner and faster. (Ivan Enderlin, 2013-06-07)

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Merge remote branch 'library-praspel/master'