creating new `env` to store the multiloadr

[donyunardi]

This is another alternative for #18.
Instead of R6, we can could create new env to store multiloadr

packages <- list(
  "package_a" = "path_to_package_a",
  "package_b" = "path_to_package_b"
)
multiloadr <- list2env(packages)
for (i in names(multiloadr)) {
  print(multiloadr[[i]])
}

However, this implies that the user will need to manually provide a list of packages rather than having a function available to automate the process of preparing the list of packages.