Reformat autocomplete's API docs.

Fix brokenness with empty queries.

Improve filter/highlighter performance for empty queries by returning results immediately. [Fixes #2529949]

Rename wordOccurrence*() to subWordMatch*() and add accent-folding versions.

Refactor the way results are passed to filters, highlighters, and formatters. [Fixes #2529522] Previously, result filters received an array of raw results, highlighters received an array of text result strings, and formatters received several arrays containing different result formats. This commit changes this behavior: filters, highlighters, and formatters now all receive a single array of result objects. Each object has several properties (display, highlighted, raw, text) representing the various formats of a given result. Filters are expected to return an array of result objects. Highlighters should return an array of highlighted result text strings. Formatters should return an array of HTML strings or Node instances.

Reorganize the AutoComplete class hierarchy to make way for widgets. Class name changes are as follows: - AutoComplete => AutoCompleteBase - AutoComplete.Filters => AutoCompleteFilters - AutoComplete.Highlighters => AutoCompleteHighlighters

Promote autocomplete out of the sandbox.