Consider `check_trailing_bits=false` for BASE64_MIME decoder about data-encoding HOT 1 CLOSED

There's at least 3 options:

• The solution in staktrace/mailparse#96 which is to define their own encoding with lazy-static.
• Using data-encoding-macro which doesn't need lazy-initialization because it produces the encoding at compile-time (see below for a snippet).
• Add a BASE64_MIME_PERMISSIVE constant in data-encoding. (I'm not willing to change the behavior of BASE64_MIME because this would be a breaking change. But adding a new constant for those who need to ignore trailing bits is fine.)

const BASE64_MIME_PERMISSIVE: data_encoding::Encoding = data_encoding_macro::new_encoding! {
    symbols: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
    padding: '=',
    check_trailing_bits: false, // NEW (defaults to true)
    wrap_width: 76,
    wrap_separator: "\r\n",
};

What do you think? Happy to add BASE64_MIME_PERMISSIVE if that's what you would prefer.

from data-encoding.