Add support for named excerpts

[chipbite]

Is your feature request related to a problem? Please describe.
Support for named excerpts, which enable a confluence page to define several excerpts exposed for other pages to include.

Describe the solution you'd like
The excerpt and excerpt-include macros add name attribute to support named excerpts.

Describe alternatives you've considered
Only using one excerpt per page.

Ref: #277

[mrueg]

Could you provide a documentation link from Confluence where they have support for named macros? Ideally with a link to the storage format.

[chipbite]

This is using confluence cloud.

Editor pics

Creating named excerpts:

Results in a page:

Consuming named excerpts

Here is the page consuming the named excerpts:

Published it looks like this:

Page source

I will see if I can get the page sources as well.