Log Message:
Update to 0.8.3

Upstream changes:
Version 0.8.3
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* Added an argument `filename` to evaluate() and parse_all() (thanks,
  @flying-sheep, #58).

Version 0.8
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* Changed package license to MIT.

Version 0.7.2
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* replay() fails to replay certain objects such as NULL (#53).

Version 0.7
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* R 3.0.2 is the minimal required version for this package now.

Version 0.6
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* Plots are no longer recorded when the current graphical device has been
  changed, which may introduce issues like yihui/knitr#824.

* `parse_all()` can parse R code that contains multibyte characters correctly
  now (#49, yihui/knitr#988)