Add feature to add and rename tags for specific paths and operations

[fabsrc]

In #2 a feature to add tags to all operations of an API was introduced. This feature (as well as renaming tags) may also be useful for specific paths and operations.

Implementation Details

• Extend renameTags and addTags functions to allow renaming and adding of tags of specific paths and operations.

• Possible configuration syntax:

  For a single path

   {
     "apis": [
       {
         "url": "http://petstore.swagger.io/v2/swagger.json",
         "paths": {
           "/pet": {
             "tags": {
               "add": [
                 "animal"
               ],
               "rename": {
                 "pet": "creature"
               }
             }
           }
         }
       }
     ]
   }

  For a single operation

   {
     "apis": [
       {
         "url": "http://petstore.swagger.io/v2/swagger.json",
         "paths": {
           "/pet": {
             "post": {
               "tags": {
                 "add": [
                   "animal"
                 ],
                 "rename": {
                   "pet": "creature"
                 }
               }
             }
           }
         }
       }
     ]
   }

• Extend test suite

• Add documentation to README