Rib does not create intermediate directories when generating post HTML

[srid]

Viz.:

[Rib] Serving at http://localhost:8080                               
# a/static/README.md                                                 
# a/2019/12/26.md                                                    
*** Exception: Error when running Shake build system:                
  at action, called at src/Development/Shake/Forward.hs:111:5 in shak
e-0.18.3-94gZtzt3YtDAYX9Ox6TYrO:Development.Shake.Forward            
* Raised the exception:                                              
b/2019/12/26.html: openFile: does not exist (No such file or directory)