Bump to 0.9.21 and year 2019, incl. Manifest fixes

pom.xml

@@ -7,7 +7,7 @@
 	<description>eBUS core library - This library handles the communication with heating engineering via the BUS specification. This protocol is used by many heating manufacturers in Europe.</description>
 	<groupId>de.cs-dev.ebus</groupId>
 	<artifactId>ebus-core</artifactId>
-	<version>0.9.20-SNAPSHOT</version>
+	<version>0.9.21-SNAPSHOT</version>
 	<url>https://github.com/csowada/ebus</url>
 	<packaging>bundle</packaging>
 
@@ -49,7 +49,7 @@
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		<maven.compiler.source>1.8</maven.compiler.source>
 		<maven.compiler.target>1.8</maven.compiler.target>
-		<license.year>2018</license.year>
+		<license.year>2019</license.year>
 	</properties>
 
 	<build>
@@ -66,6 +66,8 @@
 						<Bundle-Name>${project.name}</Bundle-Name>
 						<Bundle-Version>${project.version}</Bundle-Version>
 						<Export-Package>de.csdev.ebus.*</Export-Package>
+						<opt>resolution:=optional</opt>
+                        <Import-Package>org.slf4j;$[opt], com.fazecast.jSerialComm;$[opt], gnu.io;$[opt], *</Import-Package>
 					</instructions>
 				</configuration>
 			</plugin>
@@ -222,7 +224,7 @@
 		<dependency>
 			<groupId>commons-io</groupId>
 			<artifactId>commons-io</artifactId>
-			<version>2.5</version>
+			<version>2.2</version>
 		</dependency>
 
 		<dependency>