Support predefined ABNF core rules

[smmoosavi]

there are core rules for ABNF which are not supported in pest (e.g. SP, ALPHA). I tried the output in pest playground and got an error. I think core rules should be added by default into pest when used in abnf

[Nadrieril]

ah yeah i didn't add these because i didn't need them at the time. this project is mostly unmaintained sorry, you can make a PR and i'll look it over