changes based on reviewer feedback

Author: topepo

NEWS.md

@@ -2,6 +2,8 @@
 
 * Added a convenience function, `brulee_mlp_two_layer()`, to more easily fit two-layer networks with parsnip.  
 
+* Various changes and improvements to error and wanring messages. 
+
 # brulee 0.3.0
 
 * Fixed bug where `coef()` didn't would error if used on a `brulee_logistic_reg()` that was trained with a recipe. (#66)