Hide Kiba classes from the ETL evaluation scope

[thbar]

While testing Kiba 2.0.0.rc1 on a client codebase, I met a situation where a client-declared module named DSLExtensions was shadowed by the new Kiba::DSLExtensions containing the new Config.

Before this PR, the Parser (calling instance_eval) was declared like this:

module Kiba
  module Parser
  end
end

As I discovered, just changing the declaration to this instead:

module Kiba::Parser
end

seems to hide the Kiba classes further enough to avoid the conflict mentioned above.

I expect that a better blank-slate approach will likely be needed at some point in the future, but this seem to be good enough for the upcoming v2, and will at least make sure that clients using the DSLExtensions module to group DSL extensions (very commonly used by my clients) won't see a conflict due to the introduction of Kiba::DSLExtensions::Config.