Collective.lazysizes

--------------------

- Use data URI scheme for image placeholder to save one additional request (closes `8`_).
[hvelarde]

- Brazilian Portuguese and Spanish translations were added.
[hvelarde]

- Deal better with <img> tags with no `src` attribute;
log an error message with the request URL (closes `11`_).
[hvelarde]

- Package is now compatible with Plone 5.
[hvelarde]

- Remove dependency on Products.CMFQuickInstallerTool.
[hvelarde]

- Update lazysizes and respimg polyfill extension to v1.5.0.
[hvelarde]

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- Add option to list class identifiers that will not be processed for lazy loading.
`<img>` and `<iframe>` elements with that class directly applied to them, or to a parent element, will be skiped (closes `5`_).
[rodfersou, hvelarde]

- Update lazysizes and respimg polyfill extension to v1.4.0.
[hvelarde]

- Use a blank image instead of a spinner as placeholder.
[hvelarde]

- Logging now uses `debug` level instead of `info`.
[hvelarde]

------------------

- Initial release.

.. _`5`: https://github.com/collective/collective.lazysizes/issues/5
.. _`8`: https://github.com/collective/collective.lazysizes/issues/8
.. _`11`: https://github.com/collective/collective.lazysizes/issues/11
.. _`15`: https://github.com/collective/collective.lazysizes/issues/15
.. _`17`: https://github.com/collective/collective.lazysizes/issues/17
.. _`20`: https://github.com/collective/collective.lazysizes/issues/20