Add pluralize() function.

[gaborcsardi]

With the usual syntax and collapsed vectors.

> # Regular plurals
> nfile <- 0; pluralize("Found {nfile} file{?s}.")
Found 0 files.
> nfile <- 1; pluralize("Found {nfile} file{?s}.")
Found 1 file.
> nfile <- 2; pluralize("Found {nfile} file{?s}.")
Found 2 files.
> 
> # Irregular plurals
> ndir <- 1; pluralize("Found {ndir} director{?y/ies}.")
Found 1 directory.
> ndir <- 5; pluralize("Found {ndir} director{?y/ies}.")
Found 5 directories.
> 
> # Use 'no' instead of zero
> nfile <- 0; pluralize("Found {no(nfile)} file{?s}.")
Found no files.
> nfile <- 1; pluralize("Found {no(nfile)} file{?s}.")
Found 1 file.
> nfile <- 2; pluralize("Found {no(nfile)} file{?s}.")
Found 2 files.
> 
> # Use the length of character vectors
> pkgs <- "pkg1"
> pluralize("Will remove the {pkgs} package{?s}.")
Will remove the pkg1 package.
> pkgs <- c("pkg1", "pkg2", "pkg3")
> pluralize("Will remove the {pkgs} package{?s}.")
Will remove the pkg1, pkg2, and pkg3 packages.
> 
> pkgs <- character()
> pluralize("Will remove {?no/the/the} {pkgs} package{?s}.")

> pkgs <- c("pkg1", "pkg2", "pkg3")
> pluralize("Will remove {?no/the/the} {pkgs} package{?s}.")
Will remove the pkg1, pkg2, and pkg3 packages.
> 
> # Multiple quantities
> nfiles <- 3; ndirs <- 1
> pluralize("Found {nfiles} file{?s} and {ndirs} director{?y/ies}")
Found 3 files and 1 directory
> 
> # Explicit quantities
> nupd <- 3; ntotal <- 10
> cli_text("{nupd}/{ntotal} {qty(nupd)} file{?s} {?needs/need} updates")
3/10 files need updates

Closes #152.

[codecov-commenter]

Codecov Report

Merging #155 into master will increase coverage by 0.27%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
+ Coverage   79.34%   79.61%   +0.27%     
==========================================
  Files          30       30              
  Lines        1491     1511      +20     
==========================================
+ Hits         1183     1203      +20     
  Misses        308      308              

Impacted Files	Coverage Δ
R/pluralize.R	88.52% <100.00%> (+5.59%)	⬆️

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