v0.10.8

• feat(atom): Implement Atom save hook (#472) (3ef3bc3), closes #399
• fix(atoms): Avoid rerendering atoms when section content changes. (#471) (a59ae74), closes #421
• fix(placeholder): Use '__has-no-content' class name to display placeholder text (#461) (11452fe), closes #407 #171
• refactor(tests): Refactor deletion tests to be terser (#469) (eeb9e19)

Possible BREAKING CHANGE: The placeholder text is now absolutely
positioned (at top: 0) of the editor div. If a user has applied their
own padding to the editor div the placeholder may not show up in the
correct location. The solution is to add a CSS rule that overrides the
top to match the value of the padding-top:

.__mobiledoc-editor.__has-no-content:after {
  top: <value of padding-top>;
}

Also: The editor now has a min-height: 1em;
to ensure that the placeholder has a space in which to be displayed.