Fix for #90 - removing Enum.HasFlags

This is a perf improvement of about 500ms for our razor code generation
benchmark on my dev box. That's about .8% of the overall execution time of
this benchmark.

This change will remove a bunch of unnessary allocations from the
parsing/code-generation path, and should improve responsiveness.

For reference Enum.HasFlags performs boxing of the enum value, and then
does a type comparison to see if the types are the same. This is
significantly more costly than a normal bitwise and comparison, and it
results in allocations.
It actually seems to matter right now. going to follow up on that.

It seemed better just to change it all, and make it easy to ctrl+shift+F