Minor bug fixes and release patch version v1.9.1

[sachinstl]

Summary

This branch fixes issues #236, #237, #238 and prepares the patch version v1.9.1 for CRAN release.

Changes

The changes made in this PR are:

1. Improvement: We can remove x-axis label in this special case, where hrvar is set to NULL. Issue in the create_boxplot when hrvar is set to NULL #236
2. Improvement: Change the plot title according to the metric when metric has single value. Issue in create_stacked when metrics set to one metric then as well it shows collaboration hours  #237
3. Improvement: We can add input validation to ensure the data is a data frame, predictors are columns in the data, and outcome is a binary variable in the data. Issue in create_IV : function doesn't validate the inputs #238

Checks

• All R CMD checks pass
• roxygen2::roxygenise() has been run prior to merging to ensure that .Rd and NAMESPACE files are up to date.
• NEWS.md has been updated.

Notes

This fixes #236, #237, #238

Incorporated changes:

1. After fix on bug Issue in the create_boxplot when hrvar is set to NULL #236:

create_boxplot(sq_data, metric = "Collaboration_hours", hrvar = NULL, return = "plot")

2. After fix on bug Issue in create_stacked when metrics set to one metric then as well it shows collaboration hours  #237

sq_data %>% 
  create_stacked(hrvar = "FunctionType", 
                 metrics = "Meeting_hours", 
                 return = "plot" 
                 ) 

3. After fix on bug Issue in create_IV : function doesn't validate the inputs #238

sq_data %>%
     create_stacked(hrvar = "FunctionType",
                    metrics = c("Meeting_hours"
                                ),
                    return = "plot",
                    plot_title = "Collaboration Hours",
                    rank = "ascending")

[martinctc]

v1.9.1 has been accepted into CRAN, now merging this PR. Thanks for the changes @sachinstl!