Implement dictionary type

[marcoscaceres]

http://www.w3.org/TR/WebIDL/#idl-dictionary

[marcoscaceres]

started work on dictionary type.

[marcoscaceres]

Dictionary is quite tricky, as it requires taking in a definition of the dictionary and using that as the basis for type checking and conversion.

[FremyCompany]

Based on what I see, you can't build a generic converter from a dictionnary. So, we'll have to generate the converter code at the same time we generate the dictionnary interface.

[FremyCompany]

This issues depends on #84 (converter auto-generation) and #83 (symbol table generation).