smarter script for creating Android project

1、You can add the create-android-project.sh  to the PATH, so you can run it to create android project in the current directory if you like. Inaddition, you can put  the script anywhere you like and run it by using ./create-android-project.sh.
2、After launching the script, you can just press enter to create a default project and then call the build_native.sh to compile it.
3、Environment variables: NDK_ROOT、ANDROID_SDK_ROOT、COCOS2DX_ROOT 
are needed, or you can set them in the script.


For example:



![2013-06-04-224030_516x299_scrot](https://f.cloud.github.com/assets/781616/606146/c8663afc-cd24-11e2-86fa-42eb122a813a.png)

That's all.