Add features to VM based hom search

[kris-brown]

As mentioned in #830 there are some more features that would be nice to have for VM hom search, not limited to:

• Handle attributes, initial/monic/etc. constraints
• Sample random codomains and optimize the compiled program
• Convert program into an actual julia function rather than interpreting the VM
• Load instruction has f as a symbol, so dynamic dispatch used. This could be made static.