Feature Request: Measure line

[shannonturner]

From Youtube:

As someone who has been obsessed with making maps in your site the past three months, it's very exciting to see the new changes! Just a suggestion: Is it possible to add a measure line feature? The only downside for me is having to count the squares so everything is well distributed :p

Thematically feels related to #34, and maybe will be part of the select feature, telling you how many squares you get w/h.