Don't print 168^W143 lines of help when someone makes a typo.

Print actual usage messages in most cases.

Add --help and --version.

Bug: http://b/28054087
Test: manual
Change-Id: I39c1cb7a84f52e0c35d24f140ec55c3a181283fb
diff --git a/adb/adb_utils.cpp b/adb/adb_utils.cpp
index 5a3b401..7afa616 100644
--- a/adb/adb_utils.cpp
+++ b/adb/adb_utils.cpp
@@ -313,3 +313,15 @@
 void AdbCloser::Close(int fd) {
     adb_close(fd);
 }
+
+int usage(const char* fmt, ...) {
+    fprintf(stderr, "adb: ");
+
+    va_list ap;
+    va_start(ap, fmt);
+    vfprintf(stderr, fmt, ap);
+    va_end(ap);
+
+    fprintf(stderr, "\n");
+    return 1;
+}