0.3.1

Feature: Adds a jk validate command (#279)
Feature: Adds a jk transform command (#257)
Fix: Runtime messages are now output to stderr, leaving stdout for printing results only (#281)

Change: After #281, std.log outputs to stderr, and does not accept formatting options. Use std.print(value, options?) to print values to stdout. This is not considered a breaking change as std.log behaviour was left (largely) undefined.