Fix and test buffer reuse (ohler55#91)

changelog

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More script operators (ohler55#87)

* WIP

* Add the JSONPath 'in' operator

* Add empty filter operator

* Add empty filter operator

* Add regex filter

* changelog

* Fix linter warnings

* Add golangci cinfig file

Improve coverage

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Fix []byte encoding

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Make jp.Script thread safe

Fix parser reuse for callbacks and channels