Fixed languages.json

I've removed a few unsupported languages from `languages.json` and renamed some other languages. In summary;

### Removed Languages

* c
* gherkin
* livescript
* make
* sass
* scheme
* yaml

### Renamed Languages

* c# -> cs
* objc -> objectivec

As the current languages are not support by [highlight.js](https://github.com/isagalaev/highlight.js), attempting to run docco against any of the matching files (or by specifying the language explicitly) was resulting in the following error:

```
[neocotic docco]$ ./bin/docco ~/example.ls

/home/neocotic/dev/docco/node_modules/highlight.js/highlight.js:142
      if (mode.compiled)                                          
              ^                                                   
TypeError: Cannot read property 'compiled' of undefined           
    at compileMode (/home/neocotic/dev/docco/node_modules/highlight.js/highlight.js:142:15)
    at compileLanguage (/home/neocotic/dev/docco/node_modules/highlight.js/highlight.js:213:5)
    at highlight (/home/neocotic/dev/docco/node_modules/highlight.js/highlight.js:362:5)      
    at format (/home/neocotic/dev/docco/docco.js:96:14)                                       
    at /home/neocotic/dev/docco/docco.js:35:11                                                
    at fs.js:266:14                                                                          
    at Object.oncomplete (fs.js:107:15)
```