Switch to Method::Signatures::Simple

Method::Signatures depends on Data::Alias, which has been broken since
5.17.2 and shows no sign of being fixed by 5.18.
fixes #14
fix changelog
Merge branch 'pr/14'
v1.2.0

 [API CHANGES]

 [BUG FIXES]

 [DOCUMENTATION]

 [ENHANCEMENTS]
 - Move to Method:::Signature::Simple as M::S doesn't work with 5.17.11.
    (GH#14, ilmari)

 [NEW FEATURES]

 [STATISTICS]