Add glm engine for linear_reg()

[juliasilge]

Closes #623

library(parsnip)

linear_reg() %>% 
  set_engine("glm") %>%
  translate()
#> Linear Regression Model Specification (regression)
#> 
#> Computational engine: glm 
#> 
#> Model fit template:
#> stats::glm(formula = missing_arg(), data = missing_arg(), weights = missing_arg(), 
#>     family = stats::gaussian)

^{Created on 2021-12-13 by the reprex package (v2.0.1)}

[juliasilge]

We can pass in expressions to the family engine argument:

library(parsnip)

spec1 <- 
  linear_reg() %>% 
  set_engine("glm", family = statmod::tweedie) 

spec1 %>% translate()
#> Linear Regression Model Specification (regression)
#> 
#> Engine-Specific Arguments:
#>   family = statmod::tweedie
#> 
#> Computational engine: glm 
#> 
#> Model fit template:
#> stats::glm(formula = missing_arg(), data = missing_arg(), weights = missing_arg(), 
#>     family = statmod::tweedie)

spec1 %>% fit(breaks ~ ., data = warpbreaks)
#> parsnip model object
#> 
#> 
#> Call:  stats::glm(formula = breaks ~ ., family = ~statmod::tweedie, 
#>     data = data)
#> 
#> Coefficients:
#> (Intercept)        woolB     tensionM     tensionH  
#>      39.278       -5.778      -10.000      -14.722  
#> 
#> Degrees of Freedom: 53 Total (i.e. Null);  50 Residual
#> Null Deviance:       9233 
#> Residual Deviance: 6748  AIC: NA

spec2 <- 
  linear_reg() %>% 
  set_engine("glm", family = stats::poisson(link = "sqrt")) 

spec2 %>% translate()
#> Linear Regression Model Specification (regression)
#> 
#> Engine-Specific Arguments:
#>   family = stats::poisson(link = "sqrt")
#> 
#> Computational engine: glm 
#> 
#> Model fit template:
#> stats::glm(formula = missing_arg(), data = missing_arg(), weights = missing_arg(), 
#>     family = stats::poisson(link = "sqrt"))

spec2 %>% fit(breaks ~ ., data = warpbreaks)
#> parsnip model object
#> 
#> 
#> Call:  stats::glm(formula = breaks ~ ., family = ~stats::poisson(link = "sqrt"), 
#>     data = data)
#> 
#> Coefficients:
#> (Intercept)        woolB     tensionM     tensionH  
#>      6.2620      -0.5059      -0.8545      -1.3644  
#> 
#> Degrees of Freedom: 53 Total (i.e. Null);  50 Residual
#> Null Deviance:       297.4 
#> Residual Deviance: 212.7     AIC: 495.3

^{Created on 2021-12-13 by the reprex package (v2.0.1)}

[juliasilge]

I added a tiny translate() example about the engine argument, and did the same for logistic_reg() to close #619.

[github-actions]

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