Vim: Highlight `FOObar` as a type instead of a global constant

[xfcasio]

As the title suggests, highlight types that start with multiple capitalized characters as user types instead of global constants.

[lerno]

I recommend:

syn match c3UserType display "_*[A-Z][A-Z0-9_]*[a-z][a-zA-Z0-9_]*"

And a user defined attribute should hav the same regex but start with @, so could you please update that one as well?

[xfcasio]

good now?