Include float.h for DBL_EPSILON

https://bugs.gentoo.org/show_bug.cgi?id=480272

Patch was written by Jeroen Roovers <jer@gentoo.org>
Add missing return after error reporting.
Fix userguide formatting (Thanks Slava)
Revert "raise fullscreen windows on top of all other X11 windows"

This reverts commit 0659a0d98ca98fcd134c277c6a61ca3c9a04544e.

It was a fix for dzen2 setups, but broke several other use cases.
Because dzen2 is not really important since most people use i3bar
nowadays, let’s revert this.

fixes #1062
fixes #1068
fixes #1070
Bugfix: update root geometry on output changes for “fullscreen global” (Thanks kaersten)

fixes #1064
Bugfix: don’t flatten tabbed/stacked containers

fixes #1053
Bugfix: correctly recognize assigned windows as urgent (Thanks jookia)

fixes #1086
Reply to _NET_REQUEST_FRAME_EXTENTS correctly

Reply to _NET_REQUEST_FRAME_EXTENTS by settings _NET_FRAME_EXTENTS
property of the window to widths of the respective borders added by i3.

fixes #1093
fixes #1069
Fixed i3bar rendering and implemented inset windows in i3
Added window inset config option and command

This patch adds:
    'new_window inset <number>'
    'new_float  inset <number>'

and the command:
    'inset <number>'

Ex.
new_float inset 4
bindsym $mod+h inset 2
Added enable_alpha_channel option

This enables true 32-bit alpha support for i3 ( This is mainly nessisary
for the inset window's patch, as it fixes issues with graphical
glitches)

To use, put this:
enable_alpha_channel yes

in your config file