Tidy up structure of briefcase

I had a spare fifteen minutes and decided that I should tidy up my
monorepo. The work of tidying up is not finished; this is a small step in the
right direction.

TL;DR
- Created a tools directory
- Created a scratch directory (see README.md for more information)
- Added README.md to third_party
- Renamed delete_dotfile_symlinks -> symlinkManager
- Packaged symlinkManager as an executable symlink-mgr using buildGo

scripts/delete_dotfile_symlinks.go

@@ -1,117 +0,0 @@
-// Find and delete all symlinks to the dotfiles defined in $BRIEFCASE.
-//
-// Oftentimes I corrupt the state of my dotfiles. The intention with this script
-// is to write some tooling to help me better manage my dotfile cleanliness. An
-// example workflow might look like:
-//
-// ```shell
-// > go run delete_dotfile_symlinks.go --audit
-// > go run delete_dotfile_symlinks.go --seriously
-// > cd ..
-// > make install
-// ```
-//
-// Outstanding TODOs:
-// - Package this with <depot>buildGo.nix.
-// - How can this be run as script without `go run`? She-bang at the top?
-// - See TODOs within this package.
-
-package main
-
-import (
-	"errors"
-	"flag"
-	"fmt"
-	"log"
-	"os"
-	"path/filepath"
-	"strings"
-)
-
-// Wanted for go tooling:
-// 1. jump-to-def
-// 2. documentation at point
-// 3. autocompletion
-
-// TODO: Consider adding this to a utils.go package.
-func failOn(err error) {
-	if err != nil {
-		log.Fatal(err)
-	}
-}
-
-// TODO: Consider adding this to a utils.go package.
-func isSymlink(m os.FileMode) bool {
-	return m&os.ModeSymlink != 0
-}
-
-var hostnames = map[string]string{
-	os.Getenv("DESKTOP"):  "desktop",
-	os.Getenv("LAPTOP"):   "work_laptop",
-	os.Getenv("CLOUDTOP"): "cloudtop",
-}
-
-func main() {
-	audit := flag.Bool("audit", false, "Output all symlinks that would be deleted. This is the default behavior. This option is mutually exclusive with the --seriously option.")
-	seriously := flag.Bool("seriously", false, "Actually delete the symlinks. This option is mutually exclusive with the --audit option.")
-	repoName := flag.String("repo-name", "briefcase", "The name of the repository.")
-	deviceOnly := flag.Bool("device-only", false, "Only output the device-specific dotfiles.")
-	flag.Parse()
-
-	if !*audit && !*seriously {
-		log.Fatal(errors.New("Either -audit or -seriously needs to be set."))
-	}
-	if *audit == *seriously {
-		log.Fatal(errors.New("Arguments -audit and -seriously are mutually exclusive"))
-	}
-
-	home, err := os.UserHomeDir()
-	failOn(err)
-	count := 0
-
-	err = filepath.Walk(home, func(path string, info os.FileInfo, err error) error {
-		if isSymlink(info.Mode()) {
-			dest, err := os.Readlink(path)
-			failOn(err)
-
-			var predicate func(string) bool
-
-			if *deviceOnly {
-				predicate = func(dest string) bool {
-					var hostname string
-					hostname, err = os.Hostname()
-					failOn(err)
-					seeking, ok := hostnames[hostname]
-					if !ok {
-						log.Fatal(fmt.Sprintf("Hostname \"%s\" not supported in the hostnames map.", hostname))
-					}
-					return strings.Contains(dest, *repoName) && strings.Contains(dest, seeking)
-				}
-			} else {
-				predicate = func(dest string) bool {
-					return strings.Contains(dest, *repoName)
-				}
-			}
-
-			if predicate(dest) {
-				if *audit {
-					fmt.Printf("%s -> %s\n", path, dest)
-				} else if *seriously {
-					fmt.Printf("rm %s\n", path)
-					err = os.Remove(path)
-					failOn(err)
-				}
-				count += 1
-			}
-		}
-		return nil
-	})
-	failOn(err)
-	if *audit {
-		fmt.Printf("Would have deleted %d symlinks.\n", count)
-	} else if *seriously {
-		fmt.Printf("Successfully deleted %d symlinks.\n", count)
-	}
-
-	os.Exit(0)
-}