Prefix all symbols

[agx]

There's some symbols that neither use the vm_, varnam_ or vararray_ prefix: see https://github.com/anoop142

It would be good to namespace those before the next release as we can't drop symbols afterwards and we're polluting the namespace for other libs linked by programs otherwise.

Midterm it would make sense to prefix all symbols with a single prefix (e.g. varnam_ or just v_) and bump the soname once.

[subins2000]

@agx What is the the best ideal solution for a library, all exported symbols having the same prefix? Or is it fine to have symbols with multiple common prefixes? I was looking at libvarnam's debian packaging attempt and there are a LOT on the list: https://github.com/varnamproject/packaging/blob/master/libvarnam/debian/libvarnam.symbols