* Adjust the pattern for matching tasks. The old one was too strict,
causing it to filter out perfectly valid tasks.
* Add completion of subproject names.
* Prevent subproject tasks from overwriting the main task description.
* Require `:` prefix for showing subprojects.
* Require a subproject prefix before showing subproject tasks.
* Standardize the use of completion tags.
* Rebuild the cache if it can't be read or doesn't contain the required
arrays.
