Load recommended Perl modules on demand when available

 recommended gathers a list of recommended modules and versions and provides
 means to check if they are available. It is a thin veneer around
 Module::Runtime.
 .
 There are two major benefits over using Module::Runtime directly:
 .
   * Self-documents recommended modules together with versions at the top
     of your code, while still loading them on demand elsewhere.
   * Dies if a recommended module exists but fails to compile, but
     doesn't die if the module is missing or the version is insufficient.
     This is not something that Module::Runtime offers in a single
     subroutine.