Fix missing shortcode in doc

Use new syntax for example.
Correct alias
showcase: update ucsb entry
Fixed typo in summaries description in the documentation
Github page strategy for username.github.io repos

The whole article should maybe be rewriten to have a better content flow (maybe adding a table of content), to introduce both possible strategies. But at least, the technical steps are there!
Add Ace template engine support
Add configuration option 'Title404'

Allow 'Title404' to be set for the title of the 404 page in config.*.