maven enforcer plugin, fixed site.xml and ignored eclipse metadata files

.gitignore

@@ -1 +1,3 @@
 target/
+/.settings/
+/.project

pom.xml

@@ -1428,6 +1428,26 @@
             </extension>
         </extensions>
         <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-enforcer-plugin</artifactId>
+                <version>1.4.1</version>
+                <executions>
+                    <execution>
+                        <id>enforce-maven</id>
+                        <goals>
+                           <goal>enforce</goal>
+                        </goals>
+                       <configuration>
+                           <rules>
+                               <requireMavenVersion>
+                                   <version>3.1</version>
+                               </requireMavenVersion>
+                           </rules>
+                       </configuration>
+                    </execution>
+                </executions>
+            </plugin>
             <plugin>
                 <!--
                 This plugin will collect current build number

src/site/site.xml

@@ -1,3 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
 <!--
  * Copyright (c) 2012-2015, jcabi.com
  * All rights reserved.
@@ -26,7 +27,8 @@
  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  * OF THE POSSIBILITY OF SUCH DAMAGE.
- --><project xmlns="http://maven.apache.org/DECORATION/1.3.0"
+ -->
+<project xmlns="http://maven.apache.org/DECORATION/1.3.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/DECORATION/1.3.0 http://maven.apache.org/xsd/decoration-1.3.0.xsd"
          name="jcabi-parent">