Added Sign interface

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/block/Sign.java

@@ -0,0 +1,39 @@
+
+package org.bukkit.block;
+
+import org.bukkit.Block;
+
+/**
+ * Represents either a SignPost or a WallSign
+ */
+public interface Sign extends Block {
+    /**
+     * Gets all the lines of text currently on this sign.
+     *
+     * @return Array of Strings containing each line of text
+     */
+    public String[] getLines();
+
+    /**
+     * Gets the line of text at the specified index.
+     *
+     * For example, getLine(0) will return the first line of text.
+     *
+     * @param index Line number to get the text from, starting at 0
+     * @throws IndexOutOfBoundsException Thrown when the line does not exist
+     * @return Text on the given line
+     */
+    public String getLine(int index) throws IndexOutOfBoundsException;
+
+    /**
+     * Sets the line of text at the specified index.
+     *
+     * For example, setLine(0, "Line One") will set the first line of text to
+     * "Line One".
+     *
+     * @param index Line number to set the text at, starting from 0
+     * @param line New text to set at the specified index
+     * @throws IndexOutOfBoundsException
+     */
+    public void setLine(int index, String line) throws IndexOutOfBoundsException;
+}