Support `:` as combination of `'` and `.` for rounded corners

[Toxaris]

Context: I want to render diagrams where rounded corners signal which lines are connected at crossings. For example, in the following diagram, west connects to north and east. And south connects to east. But it is clear that south does not connect to north.

^ | ---'-.--> | |

Problem: I cannot draw a diagram where west connects to both north and south because I would have to put both ' (to connect to north) and . (to connect to south) at the same position.

Proposal: Can svgbob be extended to treat : as both . and ' in these situations?

I believe that would allow to draw all 64 combinations of lines connecting at intersections, see experiments below.

All combinations

                      no straight     west-east      north-south    both straight 
                      connections     connected      connected      connections
                      -------------   -------------  -------------  -------------

        no rounded |        |               |              |              |
       connections |     --   --         -------        -- | --        ---+---
                   |        |               |              |              |

         
        north-west |        |               |              |              |
         connected |     --'  --         --'----        --'| --        --'+---
                   |        |               |              |              |


        north-east |        |               |              |              |
         connected |     --  '--         ----'--        -- |'--        ---+'--
                   |        |               |              |              |


        south-west |        |               |              |              |
         connected |     --.  --         --.----        --.| --        --.+---
                   |        |               |              |              |


        south-east |        |               |              |              |
         connected |     --  .--         ----.--        -- |.--        ---+.--
                   |        |               |              |              |


        north-west |        |               |              |              |
    and north-east |     --' '--         --'-'--        --'|'--        --'+'--
         connected |        |               |              |              |


        north-west |        |               |              |              |
    and south-west |     --:  --         --:----        --:| --        --:+---
         connected |        |               |              |              |


        north-west |        |               |              |              |
    and south-east |     --' .--         --'-.--        --'|.--        --'+.--
         connected |        |               |              |              |


        north-east |        |               |              |              |
    and south-west |     --. '--         --.-'--        --.|'--        --.+'-
         connected |        |               |              |              |


        north-east |        |               |              |              |
    and south-east |     --  :--         ----:--        -- |:--        ---+:-
         connected |        |               |              |              |


       all rounded |        |               |              |              |
       connections |     --. :--         --.-:--        --.|:--        --.+:-
 except north-west |        |               |              |              |


       all rounded |        |               |              |              |
       connections |     --: .--         --:-.--        --:|.--        --:+.-
 except north-east |        |               |              |              |


       all rounded |        |               |              |              |
       connections |     --' :--         --'-:--        --'|:--        --'+:-
 except south-west |        |               |              |              |


       all rounded |        |               |              |              |
       connections |     --: '--         --:-'--        --:|'--        --:+'-
 except south-east |        |               |              |              |


       all rounded |        |               |              |              |
       connections |     --: :--         --:-:--        --:|:--        --:+:-
                   |        |               |              |              |

All combinations (rendered)