Clean up of #12

[BBB]

Cleaned up some of the comments from @bcherny on @benjie's #12

• There's some issues still with the types that I'm hoping to solve by adding the @types/babel__traverse package.
• There's also one test error: TypeError: Property body of DeclareClass expected node to be of a type ["ObjectTypeAnnotation"] but instead got "TSTypeLiteral"

Any ideas?

[bcherny]

My guess is DeclareClass is a Flow type (which expects only Flow types as children), while TSTypeLiteral is a TS type. This might be a limitation of the walker approach in this PR, as opposed to a recursive descent approach to transforming the tree from Flow -> TS.

[benjie]

I had to work around the types quite a lot to make it work correctly; hence the ts-ignores/etc everywhere. I think some of it was down to mismatched versions, was planning to upgrade all the dependencies and try again but still have yet to find time.