Summary:
Support custom dimensions
Had to move the definition of `Dimension` from `Duckling.Dimensions.Types` to `Duckling.Types` to avoid cyclic imports between these two modules.
A sample custom dimension is in `exe/CustomDimensionExample.hs`.
Limitations of custom dimensions:
- All rules for a custom dimension must be in the same module with the definition of the custom dimension. Otherwise there will be cyclic imports, because the definition of the dimension and the rules refer to each other.
- The custom dimension must be specified when using `parse`, since there's no way to get all the existing custom dimensions.
Reviewed By: patapizza
Differential Revision: D7630360
fbshipit-source-id: 30e12dcb33611f5692c4f5949de377bf61b75e1e
