Version 0.21.0

Changes:

• ⚠️ bower.json has been removed (#277)
• ⚠️ sanctuary-type-identifiers dependency upgraded from 2.0.x to 3.0.0 (#285)
• sanctuary-type-classes dependency upgraded from 11.0.x to 12.0.0 (#285)
• sanctuary-either dependency upgraded from 1.2.0 to 2.0.0 (#285)
• sanctuary-show dependency upgraded from 1.0.x to 2.0.0 (#284)

Additions:

• $.Void (#280)
• $.JsMap (#281, #282)
• $.JsSet (#281, #282)
• $.Module (#283)