feat: support watch mode

[dwjohnston]

I would like to be able to run this with something like:

ts-interface-builder -o src/ti src/types/*.ts --watch

And have it continually recreate the -ti files, rather than have to run it manually.

[dsagal]

You can do it fairly easily using the chokidar module:

chokidar src/types/*.ts -c 'ts-interface-builder -o src/ti {path}'