Modules that provide OS-specific behaviors often need to know if the current
operating system matches a more generic type of operating systems. For example,
'linux' is a type of 'Unix' operating system and so is 'freebsd'.
This module provides a mapping between an operating system name as given by $^O
and a more generic type. The initial version is based on the OS type mappings
provided in Module::Build and ExtUtils::CBuilder (thus, Microsoft operating
systems are given the type 'Windows' rather than 'Win32').
