speed up rtf loading time

[balshetzer]

RTF loading may be too slow.

Also, it's been reported that RTF loading time is longer on startup than when later added.

[panathea]

Is this because we have to parse it on start up, unlike JSON which we parse on stroke?

[jeremy-w]

Anyone have a sample "this is way too slow" RTF dictionary to reproduce this against?

[user202729]

There's https://github.com/sammdot/plover-better-rtf (which claims to be faster)

[benoit-pierre]

Closing, #1365 + #1362 really sped things up.