fix for LH ticket #1643
passing correct target instance variable to error_messages partial
Pulled. Thanks for contributing.
Add regression test for #1370 #3
Give example for adding calculator
Believe or not but I struggled a bit with adding my own calculator to spree. As some other folks:
It's all about naming convention so why not give example just in case someone forgot it (as I did!)
Fixed instructions for building from source. GH-3