Clarify ASCII numerals in alpha_dash and alpha_num validation rules

[austincarpenter]

ASCII characters in the \p{L} regex ranges are clarified as a-z and A-Z for the alpha_dash and alpha_num validation rules. ASCII numerals in the \p{N} range (0-9) are not.

This PR adds ", and 0-9" where relevant.

[austincarpenter]

Should the alpha_dash description go one step further? I.e.:

"To restrict this validation rule to characters in the ASCII range (a-z, A-Z, 0-9, - and _), you may provide..."

I feel like most people would always opt for the :ascii variant of the rule and having the ranges comma-separated like this without describing them makes visually identifying the rules much easier.