Tiled 1.1 Alpha4 and Documentation

This week I've spent some time on updating the documentation. The page about the JSON map format was moved from the GitHub wiki, the styling of "New in Tiled 1.X" and "Future Extensions" sections was fixed and the TMX format was updated to mention how Wang tiles are stored. Many other small adjustments were made, but some big updates still remain to be done.

The new snapshot fixes a few important issues, so be sure to upgrade:

• Fixed rendering issues after changing theme color
• Bumped minimum Qt version to 5.6
• Made the "Embed in Map" checkbox persistent (#1664)
• Fixed crash when saving two new maps using the same file name (#1734)
• Fixed issues caused by paths not being cleaned (#1713)
• Windows: Fixed copy/paste pasting invalid tiles (#1736)

Unfortunately, due to working on documentation and fixing bugs, I haven't made much progress with some actual changes that are still required for Tiled 1.1. So progress felt slow, but all this needed to happen as well anyway.