add build.sh to iOS platform

Now the scripts could be used like this:

```
./build.sh --libs [all | libname] --arch [all | armv7 | arm64 etc] --mode [release | debug]
```

If I want to build a png library with arch=armv7,arm64 on debug mode, I can use it like this:

```
./build.sh --libs png --arch armv7,arm64 --mode=debug
```

Currently the scripts work well for png, zlib, curl and luajit.

For Luajit, the x86_64 and arm64 arch will be ignored by the scripts. Because the luajit doesn't support 64bit arch well on arm platform. And the iOS 64bit simulator also has a running bug.

Please test the scripts and give me more suggestions. Thanks.