Exposing a context to the executed code

[tbeseda]

Perhaps this is related to the existing issue about plugins, but for me at least it is desirable to expose some local variables to the code being run; even Node.js methods.

[bmeck]

This is related to the plugins since exposing any non-native code to a sandbox safely requires wrapping it so it does not have direct references. I think this should be considered the prerequisite before work on plugins starts. I can get around to it in the next couple of weeks hopefully.

[bmeck]

see #8