Shellfu v0.10.47 - FloatingPointError
Overview of changes:
* Completed mkusage() docstring
The docstring has long been neglected; part of it was accidentally
added to internal API. Now it's merged together and improved.
* Fixed style for pretty.sh module variables
Renamed variables inherited by pretty modules to follow CamelCase as
Shellfu style advises.
* Arbitrary PRETTY_USAGE values will now generate warning
Previously giving any undocumented value would just lead to default
behavior. Now the default behavior is invoked by `caller` value and
undocumented values will produce warning (but other than that,
behave as before).