Allow placing ziplines

[WheteThunger]

Ziplines were recently added to the game. This plugin could support two types of ziplines:

Point A to B ziplines: To place these, we would need new commands such as mazipline start and mazipline end. The start and end point would have to be in the same monument.

Zipline targets: Zipline targets would automatically be connected to nearby pylons depending on the angle. This could be added using the custom addons proposal (#10) within the plugin (where MA is the owner of the custom addon definition), rather than implementing a new type of addon. The plugin would have to recreate the logic to find nearby zipline launch points and connect or disconnect them as necessary when zipline targets are added/removed.