Tightening the number parsing algorithm

Tightening the number parsing algorithm

Some badly formated "numbers" could get partly parsed,
resulting in truncated results instead of raising an
error.

Examples :
 '1.2.3'      -> (double)1.2
 '2015-01-15' -> (int)2015

This patch is not perfect (ex: input can still end with a 'E', which
is forbidden by json.org doc) but should avoid non-sensically
formated input.

Tests added.