New command: "update". Parse post date for sorting

README.md also updated with new command descriptions.
Refactored template. Can say "all" in copy-files.
Template procs now a file sourced w/ dir failover.

This means you can a) delete template data from your project if you
don't need to customize it; b) only customize the HTML without
maintaining a separate copy of the default procs. Keeping projects
in sync with Tclssg's project skeleton should now be easier.