cgo passing pointer rules

[zoli]

This is causing limetext/backend#87. There is a discussion I started here but I still couldn't figure out how to solve it.

Also the actual rules are here + golang/go#12416

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[zoli]

This is closed by #13, all tests are passing. Thanks to @ricochet1k.

[zoli]

Re openning this as it was causing sublime repo fail. Moved it to its own branch for later fix

https://github.com/limetext/gopy/tree/go16-cgo-fix