Allow extending modifier builder with custom to*

[ImanMahmoudinasab]

Thank you for this awesome work.
I think letting us define custom to* methods is a must for people like me with many reused scripts:

    map("l")
      .toChromeTab("http://localhost:8080")
      .description("Launch Localhost"),

[evan-liu]

You can define functions then use in to(), e.g.

map("l")
      .to(chromeTab("http://localhost:8080"))
      .description("Launch Localhost"),

function chromeTab(url) {
  return to$(`...`)
}

I have a few examples in my config

[ImanMahmoudinasab]

Yeah this is what I end up doing. Having a consistent way of defining custom tos will be a nice to have feature, though.