Franck Verrot joins as a contributor

Signed-off-by: Julien Ponge <julien.ponge@insa-lyon.fr>
Allow `_` in number literals

From now on,

    1_234_567

is equivalent to

    1234567

and

    1_234_L

is equivalent to

    1234_L

This patch closes #11 on GitHub.
Merge pull request #60 from franckverrot/master

Allowing underscores in numbers and long numbers.