#75 Supporting module path given as string

[gunnarmorling]

This also incorporates my other fix for issue #98, i.e. when merging this PR, #99 can be closed.

[ctubbsii]

I do not think this fixes the entire bug in #75. This code still assumes that when -p is seen in the arguments, it refers to a module path. However, that is not the case when executing something like
mkdir -p:

             <configuration>                                                                         
               <executable>mkdir</executable>                                                        
               <arguments>                                                                           
                 <argument>-p</argument>                                                             
                 <argument>${project.build.directory}/generated-docs</argument>                      
               </arguments>                                                                          
             </configuration>  

[rfscholte]

This should be fixed with 3296fc8