Documentation,cmd/dlv: tidy up --help output (#1649)

* scripts: use relative path in gen-cli-docs.go

Makes gen-cli-docs.go work outside GOPATH.

* Documentation,cmd/dlv: tidy up --help output

The description of --log-dest, --log-output and --backend is very
verbose and messes up the output of --help, move it to two "additional
help" subcommands.

scripts/gen-usage-docs.go

@@ -3,10 +3,35 @@
 package main
 
 import (
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+
 	"github.com/go-delve/delve/cmd/dlv/cmds"
 	"github.com/spf13/cobra/doc"
 )
 
+const defaultUsageDir = "./Documentation/usage"
+
 func main() {
-	doc.GenMarkdownTree(cmds.New(true), "./Documentation/usage")
+	usageDir := defaultUsageDir
+	if len(os.Args) > 1 {
+		usageDir = os.Args[1]
+	}
+	root := cmds.New(true)
+	doc.GenMarkdownTree(root, usageDir)
+	// GenMarkdownTree ignores additional help topic commands, so we have to do this manually
+	for _, cmd := range root.Commands() {
+		if cmd.Run == nil {
+			doc.GenMarkdownTree(cmd, usageDir)
+		}
+	}
+	fh, err := os.OpenFile(filepath.Join(usageDir, "dlv.md"), os.O_APPEND|os.O_WRONLY, 0)
+	if err != nil {
+		log.Fatalf("appending to dlv.md: %v", err)
+	}
+	defer fh.Close()
+	fmt.Fprintln(fh, "* [dlv log](dlv_log.md)\t - Help about logging flags")
+	fmt.Fprintln(fh, "* [dlv backend](dlv_backend.md)\t - Help about the `--backend` flag")
 }