Add ST_ShortestPathTree template
Add WDO SPT 1
Add first example with illustration
Add linestrings svg (in md too)
Add U, U SPT SVGs
Finish non-limited examples
Rm TREE_ID from docs

Depends on #387
Add example for limiting by search radius
Add wiki link
Add notes
Add exercises
Fix INPUT_EDGES description for ST-SP, ST-SPT
Show that Geometry is optional in output
Add input types for ST-SP*
Merge pull request #388 from agouge/ghp-st-spt-examples

Add documentation for ST_ShortestPathTree