fix(front): Ensure exceprt is rendered before used
fix(front): Ensure exceprt is rendered before used

Original sequence of behavior
- front.excerpt was put in the page's attributes
- capture attributes
- render_excerpt renders using captured attribtes
- render_excerpt updates page's attributes
- render used the captured attributes which included the unredered
  excerpt

The previous change made things worse
- capture attributes
- render_excerpt renders using captured attribtes
- render_excerpt updates page's attributes
- render used the captured attributes which had no excerpt

Now
- capture attributes
- render_excerpt renders using captured attribtes
- render_excerpt updates page's attributes
- capture attributes
- render used the updated captured attributes, including support for
  excerpt

cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs