Add support for constants or better global initialization

[hkalodner]

Currently we're using global variables as constants, ex. pristineAccount in accounts.mini. This is awkward to handle since there is not way to initialize them with a set value. It would be great if we could either support constants where the value can be initialized at compile time, or support module initialization functions that would be the first code a VM ran and could initialize the globals like init functions in go.

[edfelten]

This is high on the list of features to add.

There are pros and cons of the two approaches. Constants are simpler to do but less flexible. Initializers are more powerful, especially if they can call into other modules, but then we would need a way to avoid circularities.