Links from content or other need-parameter

[danwos]

If the content of the need is referencing other needs, these needs shall be set as outgoing links.

Example

.. spec: My spec

   This specs is based on the following specs:
  
   * :need:`SPEC_1`
   * :need:`SPEC_2` 

In this example SPEC_1 and SPEC_2 shall be set as outgoing link.

Proposal
Provide dynamic_function extract_links(need_id), which returns comma-separated of found links. If need_id is not provided, current need shall be taken.