* Add Base64 library to utils

* Fix typo on Base64 padding

* Added documentation for Base64 and references from ERC1155 and ERC721

* Updated Changelog

* Fix typo in utilities doc

* use mstore8 to improve memory accesses

* use shorter strings with encodePacked

* do not use using-for syntax, for clarity

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>