Added support for polr and summary.polr for MASS

[RomanTsegelskyi]

Support for polr/summary.polr from MASS. Here are small examples:

> house.plr <- polr(Sat ~ Infl + Type + Cont, weights = Freq, data = housing)
> pander(house.plr)

Call:
polr(formula = Sat ~ Infl + Type + Cont, data = housing, weights = Freq)


-----------------------------------------------------------------------------
 InflMedium   InflHigh   TypeApartment   TypeAtrium   TypeTerrace   ContHigh 
------------ ---------- --------------- ------------ ------------- ----------
   0.5664      1.289        -0.5724       -0.3662       -1.091       0.3603  
-----------------------------------------------------------------------------

Table: Coefficients


--------------------------
 Low|Medium   Medium|High 
------------ -------------
  -0.4961       0.6907    
--------------------------

Table: Intercepts


Residual Deviance: 3479.149 
AIC: 3495.149 
> pander(summary(house.plr))

Re-fitting to get Hessian


Call:
polr(formula = Sat ~ Infl + Type + Cont, data = housing, weights = Freq)


--------------------------------------------------
      &nbsp;         Value   Std. Error   t value 
------------------- ------- ------------ ---------
  **InflMedium**    0.5664    0.10465      5.412  

   **InflHigh**     1.2888    0.12716     10.136  

 **TypeApartment**  -0.5724   0.11924     -4.800  

  **TypeAtrium**    -0.3662   0.15517     -2.360  

  **TypeTerrace**   -1.0910   0.15149     -7.202  

   **ContHigh**     0.3603    0.09554      3.771  
--------------------------------------------------

Table: Coeficients


------------------------------------------------
     &nbsp;        Value   Std. Error   t value 
----------------- ------- ------------ ---------
 **Low|Medium**   -0.4961    0.1248     -3.974  

 **Medium|High**  0.6907     0.1255      5.505  
------------------------------------------------

Table: Intercepts


Residual Deviance: 3479.149 
AIC: 3495.149 
> pander(summary(house.plr, correlation = TRUE))

Re-fitting to get Hessian


Call:
polr(formula = Sat ~ Infl + Type + Cont, data = housing, weights = Freq)


--------------------------------------------------
      &nbsp;         Value   Std. Error   t value 
------------------- ------- ------------ ---------
  **InflMedium**    0.5664    0.10465      5.412  

   **InflHigh**     1.2888    0.12716     10.136  

 **TypeApartment**  -0.5724   0.11924     -4.800  

  **TypeAtrium**    -0.3662   0.15517     -2.360  

  **TypeTerrace**   -1.0910   0.15149     -7.202  

   **ContHigh**     0.3603    0.09554      3.771  
--------------------------------------------------

Table: Coeficients


------------------------------------------------
     &nbsp;        Value   Std. Error   t value 
----------------- ------- ------------ ---------
 **Low|Medium**   -0.4961    0.1248     -3.974  

 **Medium|High**  0.6907     0.1255      5.505  
------------------------------------------------

Table: Intercepts


Residual Deviance: 3479.149 
AIC: 3495.149 

------------------------------------------------------------------------
      &nbsp;         InflMedium   InflHigh   TypeApartment   TypeAtrium 
------------------- ------------ ---------- --------------- ------------
   **InflHigh**        0.4388                                           

 **TypeApartment**   -0.009507    -0.07377                              

  **TypeAtrium**      0.02199     -0.02934       0.52                   

  **TypeTerrace**     0.007534    -0.01464       0.536         0.4166   

   **ContHigh**       0.05234      0.121        -0.1194       -0.1346   

  **Low|Medium**       0.442       0.3482       0.5828         0.4433   

  **Medium|High**      0.4732      0.4062       0.5514         0.4275   
------------------------------------------------------------------------

Table: Correlation of Coefficients (continued below)


---------------------------------------------------------
      &nbsp;         TypeTerrace   ContHigh   Low|Medium 
------------------- ------------- ---------- ------------
   **InflHigh**                                          

 **TypeApartment**                                       

  **TypeAtrium**                                         

  **TypeTerrace**                                        

   **ContHigh**        -0.1441                           

  **Low|Medium**       0.4685       0.3721               

  **Medium|High**      0.4232       0.3924      0.9172   
---------------------------------------------------------

[codecov-io]

Current coverage is 76.73%

Merging #217 into master will increase coverage by +0.17% as of 1af0dc4

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[daroczig]

Is it intentional that we do not add an extra line break between:

Residual Deviance: 3479.149 
AIC: 3495.149 

This will be rendered on the same line after pandoc conversion AFAIK.

[RomanTsegelskyi]

Fixed the comment and merged