Workaround for number_small performance on old knausj version

[pokey]

The problem

With the release of #987, the DFA performance for Cursorless+knausj went above 1s. We were able to dramatically improve performance by optimising the number_small capture in knausj in talonhub/community#993, but unfortunately it is going to be a bit painful for people to merge knausj, given several recent large changes (eg talonhub/community#947 and talonhub/community#897). In addition, people may not even know that a knausj merge is necessary; they'll just notice that Talon periodically stalls for a DFA recompile and not know why.

The solution

We propose to do the following:

• Create our own number_small capture and use it instead of the knausj number_small when the Cursorless tag is active
• Add a tag that allows users to switch to their own number_small capture, in case they have customised it, and only use our custom capture if this tag is disabled (which it will be by default)
• Add a docs page about how to use a custom number_small, and mentioning DFA performance
• Detect that users have a custom number_small capture, and pop up a link to docs page