Add looping/replication instruction

[zippy]

We need an instruction for creating a looping construct (what we call replication) that:

1. adds an execution context for each time through the loop (i.e. like a block for any locally scoped variables.)
2. Runs serially or in parallel
3. Runs on either a collection as input parameters, or a boolean process as a conditional test for ending the replication, or for a number of times.

[zippy]

9bfb524 adds scaffolding for replication.

[zippy]

We need to figure out what replication returns, the value from the last iteration? a value via some kind of RETURN op, or yet something else, like no meaningful return value.

[zippy]

09ef5c4 adds two types of end condition for replication:

• if the condition parameter first evaluates to an INTEGER it assumes this is a simple do n times type replication, and just runs the replication code that many times.
• if the condition parameter first evaluates to a BOOLEAN, then assumes that condition should be tested every time, and runs the replication while the boolean is true