[Router] added appending of new optional document fragment

added a new optional parameter to the generate method for the document fragment. when specified this is appended to generated urls.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | none
because it is a string, there is no natural divider that we can use to represent arrays.