Morpher to snap edges that are close to each other

[luukvdmeer]

Is your feature request related to a problem? Please describe. We have a lot of network cleaning functions implemented as spatial morphers now. One thing I am missing is a solution to Case I of the following:

Hence, edges are badly mapped which makes that they end just before they meet the other edge, resulting in a poorly connected network. Case II in the image is similar and could be supported additionally by changing a function argument for example. Case III is more related to map matching, see #114

In sf there is the function st_snap which could help here, but it needs quite some tuning. Open for ideas!