Pycvodes

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- Expose set_max_steps_between_jac

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- Fix parallel adaptive wrt ew_ele array (triple pointer -> double pointer).

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- Add compile time option "PYCVODES_CLIP_TO_CONSTRAINTS" (currently defaults to 0).
To handle polynomial interpolatino from sundials giving negative values even when
using positive constraints.

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- Support for sundials>=4.0.0

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- Fix signature in header

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- Fix syntax error in header file