Dialog can be showed or hidden with custom action
Added support for multiple recipients.
Slightly changed State API to properly support multiple recipients.
Added angle calculation methods to Vector2

Added two methods to the Vector2 class, allowing to calculate angle between two vectors, and not only between the x-axis.

I'm not using the standard acos solution, math explained here: http://geomalgorithms.com/vector_products.html

Since the dot product is the cosine of the angle between two vectors, and the 2d cross product (perp dot) is the sine of the same angle, plugging both on a `atan2(crs, dot)` call can give the angle on the full circle (-180~+180, instead of `acos(dot)` solution, which gives only 0~180) and also avoid the two sqrts involved in normalising the vectors.

Here's another explanation on the matter: http://johnblackburne.blogspot.com.br/2012/01/angle-between-two-vectors.html
Update Vector2.java

shouldn't have a conversion here
add failsafe display mode and isUsingFailsafeDisplay() methods for LWJGL
add semicolon
remove isUsingFailsafeDisplay method from Graphics interface
Made the map implementations Java 8 compliant.
NateS solution for ObjectMap and IdentityMap.
Merge remote-tracking branch 'upstream/master' into failed-display
Merge branch 'master' into failed-display
use callback for display mode creation failure
Added a StateMachine which is based on a Stack.
Bugfixes.
JavaDoc fixed.
Merge pull request #2149 from jrenner/failed-display

handle display creation failure for LWJGL
Scene2d: Add positionChanged() method to Actor.
Added premultiplied alpha to particle emitter and particle editor.
Updated changes.