cli: Make tinygo help experience more consistent with go help tinygo-…

…org#3739

- Improve tinygo help command output by streamlining layout and command descriptions
- Reorganize commands and help topics alphabetically, moving info and targets to help topics
- Create a new 'flags' help topic that contains all the flag details
- Introduce gc topic to hold information related to garbage collector options
- Use 'text/tabwriter' for consistent formatting and structuring of the help output

Credit to @m-kru for layout

main.go

@@ -23,6 +23,7 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
+	"text/tabwriter"
 	"time"
 
 	"github.com/google/shlex"
@@ -1201,28 +1202,38 @@ func usage(command string) {
 	switch command {
 	default:
 		fmt.Fprintln(os.Stderr, "TinyGo is a Go compiler for small places.")
-		fmt.Fprintln(os.Stderr, "version:", version)
-		fmt.Fprintf(os.Stderr, "usage: %s <command> [arguments]\n", os.Args[0])
-		fmt.Fprintln(os.Stderr, "\ncommands:")
-		fmt.Fprintln(os.Stderr, "  build:   compile packages and dependencies")
-		fmt.Fprintln(os.Stderr, "  run:     compile and run immediately")
-		fmt.Fprintln(os.Stderr, "  test:    test packages")
-		fmt.Fprintln(os.Stderr, "  flash:   compile and flash to the device")
-		fmt.Fprintln(os.Stderr, "  gdb:     run/flash and immediately enter GDB")
-		fmt.Fprintln(os.Stderr, "  lldb:    run/flash and immediately enter LLDB")
-		fmt.Fprintln(os.Stderr, "  monitor: open communication port")
-		fmt.Fprintln(os.Stderr, "  env:     list environment variables used during build")
-		fmt.Fprintln(os.Stderr, "  list:    run go list using the TinyGo root")
-		fmt.Fprintln(os.Stderr, "  clean:   empty cache directory ("+goenv.Get("GOCACHE")+")")
-		fmt.Fprintln(os.Stderr, "  targets: list targets")
-		fmt.Fprintln(os.Stderr, "  info:    show info for specified target")
-		fmt.Fprintln(os.Stderr, "  version: show version")
-		fmt.Fprintln(os.Stderr, "  help:    print this help text")
+		fmt.Fprintf(os.Stderr, "version: %s\n\n", version)
 
-		if flag.Parsed() {
-			fmt.Fprintln(os.Stderr, "\nflags:")
-			flag.PrintDefaults()
-		}
+		fmt.Fprintln(os.Stderr, "Usage:\n")
+		fmt.Fprintln(os.Stderr, "\ttinygo <command> [arguments]\n")
+		fmt.Fprintln(os.Stderr, "The commands are:\n")
+
+		tabw := tabwriter.NewWriter(os.Stderr, 0, 0, 4, ' ', 0)
+
+		fmt.Fprintln(tabw, "\tbuild\tcompile packages and dependencies")
+		fmt.Fprintln(tabw, "\tclean\tempty cache directory (/home/mkru/.cache/tinygo)")
+		fmt.Fprintln(tabw, "\tenv\tlist environment variables used during build")
+		fmt.Fprintln(tabw, "\tflash\tcompile and flash to the device")
+		fmt.Fprintln(tabw, "\tgdb\trun/flash and immediately enter GDB")
+		fmt.Fprintln(tabw, "\thelp\tprint this help text")
+		fmt.Fprintln(tabw, "\tlist\trun go list using the TinyGo root")
+		fmt.Fprintln(tabw, "\tlldb\trun/flash and immediately enter LLDB")
+		fmt.Fprintln(tabw, "\tmonitor\topen communication port")
+		fmt.Fprintln(tabw, "\trun\tcompile and run immediately")
+		fmt.Fprintln(tabw, "\ttest\ttest packages")
+		fmt.Fprintln(tabw, "\tversion\tshow version")
+
+		tabw.Flush()
+
+		fmt.Println("\nUse \"tinygo help <command>\" for more information about a command.\n")
+		fmt.Println("Additional help topics:\n")
+		fmt.Fprintln(tabw, "\tflags\tgeneral flags")
+		fmt.Fprintln(tabw, "\tinfo\tshow info for specified target")
+		fmt.Fprintln(tabw, "\ttargets\tlist targets")
+
+		tabw.Flush()
+
+		fmt.Fprintln(os.Stderr, "\nUse \"tinygo help <topic>\" for more information about that topic.")
 
 		fmt.Fprintln(os.Stderr, "\nfor more details, see https://tinygo.org/docs/reference/usage/")
 	}
@@ -1607,6 +1618,11 @@ func main() {
 		if err != nil {
 			handleCompilerError(err)
 		}
+	case "flag":
+		if flag.Parsed() {
+			fmt.Fprintln(os.Stderr, "\nflags:")
+			flag.PrintDefaults()
+		}
 	case "flash", "gdb", "lldb":
 		pkgName := filepath.ToSlash(flag.Arg(0))
 		if command == "flash" {