docs: Documentation for command line frontend (#518)

* documentation: copied old documentation from wiki

* command: better online documentation

Help without arguments prints just a short summary for each command,
help followed by a command prints the command's syntax and a longer
explanation.

* documentation: automatically generate Documentation/cli/README.md

scripts/gen-cli-docs.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"bufio"
+	"log"
+	"os"
+
+	"github.com/derekparker/delve/terminal"
+)
+
+func main() {
+	fh, err := os.Create(os.ExpandEnv("$GOPATH/src/github.com/derekparker/delve/Documentation/cli/README.md"))
+	if err != nil {
+		log.Fatalf("could not create README.md: %v", err)
+	}
+	defer fh.Close()
+
+	w := bufio.NewWriter(fh)
+	defer w.Flush()
+
+	commands := terminal.DebugCommands(nil)
+	commands.WriteMarkdown(w)
+}