WISH: Make package lightweight by dropping dependency on 'stringr'

[HenrikBengtsson]

The 'stringr' package depends on 'stringi', which is quite heavy and takes a long time to install from source. Looking at the source code, 'beepr' uses:

• stringr::str_detect()
• stringr::str_replace_all()
• stringr::str_trim()

These can easily be replaced by base::grepl() and base::gsub(), e.g.

str_detect <- function(string, pattern, ignore_case = TRUE) {
  grepl(pattern, string, ignore.case = ignore_case)
}

str_replace_all <- function (string, pattern, replacement) {
  gsub(pattern, replacement, string)
}

str_trim <- function(string) {
  gsub("(^[[:space:]]+|[[:space:]]+$)", "", string)
}

Doing so would make 'beepr' depend on only 'audio'.

[rasmusab]

Addressed by 526fd65