Allow user to override the default values for optimize

[DilumAluthge]

This pull request allows the user to override the values of optimize that are passed to Base.code_typed.

[DilumAluthge]

Test failures on 1.2 and nightly are a known issue - see issue #31

[pfitzseb]

What's the benefit of this?
I feel like some of our passes won't work correctly with the optimized code_typed (although tests pass, but I wouldn't really want to trust that :P).

[DilumAluthge]

So, when I originally opened this PR, I was hoping that I could use it to fix the tests on 1.2. One of the test failures can be fixed by setting optimize = true.

But it didn’t end up panning out for the other test failures, so I don’t think we can use this to fix the tests.