PR for complex numbers

[paulxshen]

I needed the following to avoid errors (probably due to redundant type conversions in my code):
TrackedFloats.tf_untrack_complex(x::Complex32) = x
TrackedFloats.tf_track_complex(x::Complex{TrackedFloat32}) = x
etc...

[ashton314]

Hi there!

Please provide a complete minimal example that shows the undesired behavior, as well as a description of what you think the behavior should be.

Also, the title you gave us says "PR"—do you intend to submit a PR to fix this issue? (I've updated the title to replace # → number; please do not use # as an abbreviation. Please update further to make the title more descriptive—in particular, do not put PR unless you really intend to submit a pull request.)

[bennn]

Sounds related to #30 . It would be awesome to support more number types!