Add special attributes for paragraphs.

[NEricN]

This change also forces the @list specifier for list-level attributes. Before, any string could have been used and it would have been interpreted as a list-level special attribute.

Paragraphs that need special attributes must have the @paragraph identifier in the beginning of their special attributes. This was used because it is very common in text to have brackets, and would lead to false positives otherwise.

[codecov-io]

Current coverage is 62.17% (diff: 78.12%)

Merging #34 into master will increase coverage by 0.07%

@@             master        #34   diff @@
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  Files            14         14          
  Lines          3860       3876    +16   
  Methods         255        255          
  Messages          0          0          
  Branches       1037       1042     +5   
==========================================
+ Hits           2397       2410    +13   
+ Misses         1030       1028     -2   
- Partials        433        438     +5   

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[kjdev]

Thanks.