retry: A wrapper around `try` that retries on failure

Description

This is useful for functions that are "flaky", such as curl, which may fail for unknown reasons that do not persist.

retry(
  expr,
  envir = parent.frame(),
  retries = 5,
  exponentialDecayBase = 1.3,
  silent = TRUE,
  exprBetween = NULL,
  messageFn = message
)

As with try, so the successfully returned return() from the expr or a try-error.

expr: An expression to run, i.e., rnorm(1), similar to what is passed to try
envir: The environment in which to evaluate the quoted expression, default to parent.frame(1)
retries: Numeric. The maximum number of retries.
exponentialDecayBase: Numeric > 1.0. The delay between successive retries will be runif(1, min = 0, max = exponentialDecayBase ^ i - 1) where i is the retry number (i.e., follows seq_len(retries))
silent: Logical indicating whether to try silently.
exprBetween: Another expression that should be run after a failed attempt of the expr. This should return a named list, where the names indicate the object names to update in the main expr, and the return value is the new value. (previous versions allowed a non-list return, but where the final line had to be an assignment operator, specifying what object (that is used in expr) will be updated prior to running the expr again. For backwards compatibility, this still works).
messageFn: A function for messaging to console. Defaults to message

# retries a flaky expression; here it simply succeeds on the first try
retry(rnorm(1), retries = 3)

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