Add Global Variables.
Add a few missing, 'fairly' common classes.
Add syntax check.

Protection against older versions of Vim. Possibility supported in
future, unneeded now.

Vim occasionally misidentifies C++/ROOT to be of filetype C, due to file
endings, such as `macro.C`.

Conditional load of Typedefs, such as `Int_t`. PyROOT does not use them
due to python being a dynamically typed language.

Set `b:current_syntax` to reflect C++/ROOT vs. PyROOT.