Migration code wasn't hard to do as I expected. It was pretty straightforward, but there's some bugs that I need to fix before I can release it:
It don't correctly recognize systems that are under full influence from an empire, so no migration occurs to any other systems. I think I know the cause of this, so this should be simple to fix.
Population grows to exceed the maximum population (for example, having 104 people on 100 limit planet). There are two formulas that calculate the growth, the normal growth formula, and food abundance formula. I will need to check those and modify them so they become one formula to avoid this problem. I do have some ideas on how, so this also should be simple to fix.
But other than that, it successfully finds planets (currently, only planets from home system) that it can migrate to, and moves people during migration calculations.
After the bugs are ironed out (maybe with some other bugs from issues list in google code page), I will release it either tonight or tomorrow. Then I can start work on something that I've been looking forward for a long time, technologies/research and ship design/construction. Booyah!