* Add support for declaring arguments as repeatable
If the usage of the argument includes the phrase "Can be repeated.",
the corresponding arg_ variable will be an array containing one element
per instance of the argument.
* Add example and test for using repeated parameters
* Add example and test for using repeated flags
* better logging: support for multiple lines
* renamed logging function from _fmt to __b3bp_log
* adding example to show how multiline logging works
the main idea is to be able to log e.g. the output of a command and
b3bp taking care of splitting and prefixing every line.
* simplified code, removed hacky space-at-EOL
