Add a new journals() function to list available journal name

[cderv]

This follows an idea in #316 (review)

This new function allows to list the journal by their names

rticles::journals()
#>  [1] "acm"            "acs"            "aea"            "agu"           
#>  [5] "amq"            "ams"            "arxiv"          "asa"           
#>  [9] "bioinformatics" "biometrics"     "copernicus"     "ctex"          
#> [13] "elsevier"       "frontiers"      "ieee"           "joss"          
#> [17] "jss"            "mdpi"           "mnras"          "oup"           
#> [21] "peerj"          "plos"           "pnas"           "rjournal"      
#> [25] "rsos"           "rss"            "sage"           "sim"           
#> [29] "springer"       "tf"

^{Created on 2020-08-20 by the reprex package (v0.3.0.9001)}

The help page document the usage of this new names.

[yihui]

Thanks!