clubSandwich 0.2.2
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* Added bread() methods for all supported model classes.
* vcovCR() is now calculated using bread(), and carries attributes for bread, est_mat, and adjustment matrices.
* vcovCR() gains a 'form' argument to obtain just the meat of the sandwich, or to use a user-specified bread matrix. 
* Refactored internal functions for degrees of freedom calculation to improve speed and memory usage.
* Bug fixes:
  - updated nobs.plm method to handle first-differenced models
  

clubSandwich 0.2.1
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* First version released on CRAN.