Exportable Run function

[oliverpool]

Closes #416

This PR adds an exported Run function to the root package.

This allows this library to be simply embedded into other cli apps.

Usage is just like https://github.com/kyleconroy/sqlc/blob/main/cmd/sqlc/main.go :

package main

import (
	"os"

	sqlc "github.com/kyleconroy/sqlc/pkg/cli"
)

func main() {
	os.Exit(sqlc.Run(os.Args[1:], os.Stdin, os.Stdout, os.Stderr))
}

This does not export any internal types, but simply exposes the same interface as the CLI to any go program.

---

In my case, I have a tool folder in my go project with this file, so that I can run go run ./tool/sqlc.go and be sure to have the right version from the project's go.mod

[kyleconroy]

Can we create mirror what eabuild does and create a new pkg/cli package?

https://pkg.go.dev/github.com/evanw/esbuild/pkg/cli

[oliverpool]

@kyleconroy sure, I amended my commit.

[kyleconroy]

Can we remove the stdin, stdout, and stderr arguments? I'd like the exposed function to only take a string slice.

[oliverpool]

Like this?