Check --fields-C={properties} for static and extern attributes

[ParadoxV5]

Follow up to #6.
Currently, FFI-UCtags reads variables and functions naïvely without considering the storage classifiers.

c6811ec has hot-reverted variable loading.
Only those marked with extern or (const but not static) are available via FFI.
Note that u-ctags read const as part of the type (typeref), so it might appreciate some help from #19.

Functions, while extern by default, should also exclude static ones.