Additional arrow types

[tomyan112]

Describe the solution you'd like

Retrosynthetic arrow: Shows precursors for a given molecule

Dashed reaction arrow: shows a theoretical step(s)

Connecting arrow, allow a new arrow to be drawn from existing arrow

With a beginning- , mid-, ending- point anchor shows when pointer hovering on it

when another arrow is near the anchor point, it will attach to it example: straight arrow attach to curve arrow at mid-point

Example Different kind of curve arrow, fishhook arrow

[deadlyvices]

We can do 1 & 2 pretty easily. 3 will be more difficult.