Add option for default config file.

[Tydus]

The file is located at /spritecss.ini

I've just checked why my anneal_steps passed in css file is ignored. Then I found we should not include this option into css-per-file ones, it should be global.
So I wrote this not-so-related patch for users use the global config file more easily, without specify `-c' every time.

Signed-off-by: Tydus Tydus@Tydus.org

[lericson]

Hello @tyeken8 and thanks for your contribution!

It would make sense to have a default configuration file somewhere, but I don't think this implementation is very polished. It'll break on Windows, for example, and it'll hide lots of errors.

The default configuration should probably be loaded in addition to the specified configuration file, don't you think? I'm not sure what the best way to get to /etc files is, but it has to translate to Windows at least.

[Tydus]

Well, I tried on my windows box and it works well (with a small fix in MANIFEST.in)

D:\Spritemapper\workspace\css>spritemapper awesome-font.css
mapping sprites in source awesome-font.css
..\img\awesome-font.png
packing sprites in mapping ..\img\awesome-font.png
Temperature Energy Accept Improve Elapsed Remaining
800000.00 14740.00 0:00:00
1100.00 14740.00 100.00% 0.00% 0:00:00 0:00:00
Packed size is 110x134 (61.703% empty space)
writing spritemap image at ..\img\awesome-font.png
writing new css at awesome.css

D:\Spritemapper\workspace\css>cat C:\Python27\Scripts\spritecss.ini
[spritemapper]
anneal_steps = 1

And I'm working on a new patch for using the global and specified config files together. Come back later.