Amazon has discontinued a secretive effort to develop an at-home fertility tracker, according to internal documents and people familiar with the matter.The company had been working to launch a fertility monitoring device and companion smartphone app for the past four years as part of a project codenamed "Encore," said the people, who asked not to be named because they weren't authorized to speak to the press. The team sat within Amazon's Grand Challenge, also known as its Special Projects division, the sour ...