#70 support Perl 5.12 "package NAMESPACE VERSION BLOCK" syntax

Fix #70 with an adaptation of BDFOY's patch from https://rt.cpan.org/Public/Bug/Display.html?id=67831 , with tests.

Following the lead of PPI's parsing of statements like `use 5.020;', non-vstring version numbers are allowed to remain `PPI::Token::Number::Float`s, rather than forcing them to `PPI::Token::Number::Version`s somehow.