reading sprite config with project level

Add 'Project-level' configuration support.

http://glue.readthedocs.org/en/latest/files.html#introduction

    sprites
        ├── actions
        │   ├── add.png
        │   ├── remove.png
        │   └── sprite.conf
        └── icons
        │   ├── comment.png
        │   ├── new.png
        │   └── rss.png
        └── sprite.conf

The arguments in the sprite-level configuration file can overwrite the value of 'sprite.conf' in the project folder.

The glue DO NOT read the arguments in the 'Project-level' file after v0.9 and that's different with v0.3 before.

So I add this future back to the latest version.