enhance CPAN-Meta-Spec and reqs for 'c' suffix #104
Description
cperl added the final 'c' character as perl5-incompatible feature in the version number to denote modernized modules with signatures and types. 'c' modules are accepted by cperl, but not by perl5. non-'c' modules are accepted by cperl and perl5.
version already accepts a final 'c'. currently only detectable in the original hash key.
Now also add 'c' support to the CPAN prereq checks.
Add a permitted c suffix to version in CPAN::Meta::Spec and CPAN::Meta::Requirements.
It's okay when perl5 does not adopt this, as those two plus version are shipped with cperl core.
requirements for c versions are currently only satisfied by cperl. (signatures and types)
cperl accepts versions with and without c, and should not warn about not existing, builtin modules (XSLoader, DynaLoader, strict, attributes) or unparsable versions.
version, EUMM and CPAN was already fixed, but improve version more