tidymodels/stacks: stacks 1.0.1

Tightened integration with the workflowsets package (#161, #165). Refined logic with adding candidates via workflowsets to allow for partially trained workflow sets. In the case that a workflow set contains some failed tuning results, stacks will inform the user that they will be excluded from the data stack and only add the results that trained successfully. Extended documentation related to the packages' interactions, including a new article on the package website. Revamped errors, warnings, and messages. Prompts now provide more thorough context about where they arose, include more extensive references to documentation, and are correctly pluralized (#150, #167). blend_predictions() doesn't error anymore if the control argument isn't a control_grid object. As long as the list passed to control include the same elements as control_grid() output, parsnip::condense_control() will handle input (#149). Removes an unneeded data import attribute from the tree_frogs example data and its associated objects (#148). Various bug fixes and improvements to documentation