Move everything to a subdirectory

Also don't run cd for the initial git clone (DERP!), and other bash port fixes.

Ports/SDL2/SDL2.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+PORT_DIR=SDL
+function fetch() {
+    run_fetch_git "https://github.com/SerenityOS/SDL"
+}
+function configure() {
+    run_configure_cmake
+}
+function build() {
+    run_make
+}
+function install() {
+    run_make_install
+}
+source ../.port_include.sh