Markdown editor inline styling can fall into broken state

[erquhart]

- Do you want to request a feature or report a bug?

bug

- What is the current behavior?

Markdown editor inline marks (e.g. bold, italic) can become stuck in an active state

- If the current behavior is a bug, please provide the steps to reproduce.

• Enter text in the markdown editor
• With no text selected, activate an inline mark, such as bold
• In the same block that is currently focused, select some text and attempt to toggle inline marks

- What is the expected behavior?

• Inline marks should toggle on and off when toolbar buttons are clicked

- Please mention your CMS, node.js, and operating system version.

Confirmed in 0.6.0 and 0.7.2.

[erquhart]

Loosely related to #774 (that change did not cause this, just in the same area of concern).

If you try this in the [Slate example editor], a mark can be activated when nothing is selected, but when you highlight surrounding text, the mark is shown inactive.

I see two issues:

1. If nothing is selected, clicking an inline mark button should do nothing. This may be more of an internal Slate issue for our current, minimal implementation.
2. It seems like the root of our mishandling is how we reckon selections where only a portion of the selection has a mark.

[erquhart]

This looks to have been addressed through the Slate 0.30 upgrade.