Add tags to sketches

Nature of issue?

• Existing feature enhancement
• New feature request

Feature enhancement details:

This is midway between a modification of an existing feature (sketch name) and a new feature request.
Right now the sketch name field is auto-generated, in the manner of Pugnacious Puffin, as well as being user editable. The actual field has a capacious character limit, and could be extended to hold tags as well as a file name.

To do this, there might be a delimiter in the name field (colon and slash are obvious choices, but get replaced on may file systems. | and # could work), where everything before is the title, and everything after is a collection of space-separated tags, or in-line CSV.

I just named a file

Graceful table # expanding purple square rect rectangle 'homework 1'

and it renders and downloads fine. If such a file name could be titled and downloaded as "Graceful table" but searchable as rect, rectangle, and so on, it would offer the user valuable search capabilities wherever they store the URL (e.g. Digg or Pinboard), without db re-engineering.

(Bonus points for including tags.txt in the .zip file.)

The request concerns the sketch name field, URL-based search, downloaded filenames, and optionally tags.txt in the .zip, but it names no repository files or tests. Start by tracing how sketch names flow through search and downloads; the work is done when the tagging format, title handling, search behavior, and archive output are specified and covered by tests.