ExprYawPitch: support for entities, better description

[Mwexim]

Description

• Added support for entities, more specifically to change the yaw/pitch of an entity.
• Made the description better and more clear. Skript actually alters yaw and pitch behavior and this was not obvious to the user.
• ~~Made the code consistent. Sometimes it would use the Bukkit system, and sometimes the Skript system. Now it only uses Skript's system.~~

~~A quick overview of the differences between Skript's yaw and pitch system:~~

• ~~A yaw of 0 represents the positive x direction. Rotating by a positive number will rotate the yaw counter-clockwise.~~
• ~~A pitch of 90 represents the positive y direction. Adding a positive number to the pitch will rotate upwards.~~

Edit (@sovdeeth): I've reverted the yaw/pitch changes to ensure that the yaw/pitch will be the same before and after this PR. This means yaw is the same as Minecraft's, but always positive ( [0, 360) instead of [-180, 180) ) and that pitch is exactly the same as Minecraft.

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Target Minecraft Versions: any Requirements: N/A Related Issues: N/A