fix padding check, default ignore_newline

[kxc-ryfujis]

• should fix base64 decode padding check is inaccurate when input contains newlines #25
• part of make default base64 config ignore newline (and maybe also leading/trailing whitespaces) characters #26
  • create Config_rfc4648_relaxed and use as default

post merge task:

• make default base64 config ignore newline (and maybe also leading/trailing whitespaces) characters #26
  • config ignore (leading/trailing) whitespaces