Seperate the data types between simple and composite

[patacca]

Right now the data types are divided in "simple" (word, dword, ascii, etc...) and "structure" (structure, union, enum).
Imho this is not a good choice of words as the term "structure" could either mean a proper "structure" (like a C struct) or the collection of data types (struct, union and enum).

I propose to refactor the data types to add enum as a "simple" type (after all it's not a composite type, its fields' type are homogeneous) and rename the "structure" type to "composite". A "composite" data type would be either a struct or a union, making it in fact a heterogeneous type.

More tests need to be done to prove that a enum can effectively be moved into the "simple" types.