Types reported by `pandoc.utils.types` are inconsistent

[tarleb]

Some types have a pandoc prefix, while others do not. This should be consistent, at least for AST types.

[tarleb]

We can't add a pandoc prefix to AST types that don't have them right now, it would break many filters.

Options:

• Remove the prefix in the names of all AST types, including Row. Downside: this adds more unprefixed entries in the Lua registry, increasing the risk of name collisions with other libraries.
• Add the prefix to all names, but change pandoc.utils.types so it reports the name without the prefix. Downside: names in error messages would differ from the type name reported by pandoc.utils.types.

[wlupton]

There's also the question of separators. Currently we have (for example):

• List for pandoc.List
• pandoc Xxx for pandoc.Row etc.
• HsLua.JSON.array