title: How to merge piece by piece
body: <p>I want to merge from feature_branch to master, but not all in one piece, as that could lead to hard-to-debug problems.</p>
  
  <p>I merged some of the changes manually, pushed them to github, and did a "compare master with feature_branch" in github. I expected this to show fewer changes than before, but it didn't.</p>
  
  <p>What's the correct way to do this?</p>