Watchexec filterer: tagged

Experimental filterer using tagged filters.

• API documentation.
• Licensed under Apache 2.0.
• Status: soft-deprecated.

The tagged filterer is not in use in the Watchexec CLI, but this crate will continue being updated until and unless it becomes too much of a pain to do so, for third party users. It is expected that some of the code will eventually be reused for a more generic filter crate without the tagged syntax.