leading space in section is eaten by browser

[bantic]

Same issue as #68 but in reverse. If a textNode begins with a leading space when we position the cursor at the start of it, the space gets eaten by the browser.

Example codepen.

This can be recreated making a selection that includes the start of a section up until right before a space character, and hitting <delete>. The start of the section will not show the space, and it won't be there if you type a new character.

Using a no-break space (same fix for #68) fixes this issue as well.