Re-allow consecutive, leading and trailing dots in EMAIL_REGEXP

[osyoyu]

Effectively reverts commit 788274b and 0abac72.

EMAIL_REGEXP was mostly drawn from WHATWG HTML LS. This spec states that it intentionally violates RFC 5322 to provide a practical regex for validation.

This requirement is a willful violation of RFC 5322, which defines a syntax for email addresses that is simultaneously too strict (before the "@" character), too vague (after the "@" character), and too lax (allowing comments, whitespace characters, and quoted strings in manners unfamiliar to most users) to be of practical use here.

The allowing of consecutive dot s(a..a@) and leading/trailing dots (.a@, a.@) is not the only deviation from RFC 5322. If a truly RFC 5322-compliant regexp is needed, it should be organized under a different name, since too much departure from the original EMAIL_REGEXP must be introduced.

[moznion]

@osyoyu I think this should also be reverted because it was introduced in v1.1.0: #124

[osyoyu]

Edited. EMAIL_REGEXP is now identical to that of v1.0.4.

[sorah]

Bit hesitant to cut into this issue without waiting people involved in the original pull request, but merging this as the issue appears to have major impact.

[sorah]

While minor release (increment of Y in X.Y.Z) may have a breaking change, it must be well communicated - and the comment says it is based on WHATWG practical pattern, disallowing the email addresses in question can be considered a bug/regression. The comment on the constant mentions WHATWG even in 1.1.0, there's no doubt that this is a bug.

[osyoyu]

Thank you!