Added schema for cards.xml

doc/cards.xsd

+<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
+  <xs:element name="cockatrice_carddatabase">
+    <xs:complexType>
+      <xs:sequence>
+        <xs:element name="sets">
+          <xs:complexType>
+            <xs:sequence>
+              <xs:element name="set" maxOccurs="unbounded" minOccurs="0">
+                <xs:complexType>
+                  <xs:sequence>
+                    <xs:element type="xs:string" name="name"/>
+                    <xs:element type="xs:string" name="longname"/>
+                  </xs:sequence>
+                </xs:complexType>
+              </xs:element>
+            </xs:sequence>
+          </xs:complexType>
+        </xs:element>
+        <xs:element name="cards">
+          <xs:complexType>
+            <xs:sequence>
+              <xs:element name="card" maxOccurs="unbounded" minOccurs="0">
+                <xs:complexType>
+                  <xs:sequence>
+                    <xs:element type="xs:string" name="name"/>
+                    <xs:element name="set" maxOccurs="unbounded" minOccurs="0">
+                      <xs:complexType>
+                        <xs:simpleContent>
+                          <xs:extension base="xs:string">
+                            <xs:attribute type="xs:int" name="muId" use="optional"/>
+                            <xs:attribute type="xs:anyURI" name="picUrl" use="optional"/>
+                            <xs:attribute type="xs:anyURI" name="picUrlHq" use="optional"/>
+                          </xs:extension>
+                        </xs:simpleContent>
+                      </xs:complexType>
+                    </xs:element>
+                    <xs:element type="xs:string" name="color" minOccurs="0"/>
+                    <xs:element type="xs:string" name="manacost"/>
+                    <xs:element type="xs:string" name="type"/>
+                    <xs:element type="xs:string" name="pt" minOccurs="0"/>
+                    <xs:element type="xs:integer" name="tablerow"/>
+                    <xs:element type="xs:string" name="text"/>
+                    <xs:element type="xs:boolean" name="cipt" minOccurs="0"/>
+                    <xs:element type="xs:integer" name="loyalty" minOccurs="0"/>
+                    <xs:element type="xs:boolean" name="token" minOccurs="0"/>
+                  </xs:sequence>
+                </xs:complexType>
+              </xs:element>
+            </xs:sequence>
+          </xs:complexType>
+        </xs:element>
+      </xs:sequence>
+      <xs:attribute type="xs:integer" name="version"/>
+    </xs:complexType>
+  </xs:element>
+</xs:schema>
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