12 IPTC character encoding

The iptc CodedCharacterSet tag will be used for the encoding of iptc
tags. If not available the IptcReader will try to guess the encoding.
Indentation and simplification.
EOL whitespace
Remove unused main function.
Document fall-through of empty catch blocks.
Formatting.
Check array length to protect against IndexOutOfBoundsException.
Arguments as final.
Annotate functions for nullability.
Replace repeated statements with a loop.
Change fields from int to byte.
Javadoc formatting.
Remove incorrect explanation from @throws statements.
Document getS15Fixed16 function. Relates to #46.
Xerces dependency removed from pom.xml
Update version number of Maven plugins in pom.xml
Adds -Xdoclint:none to allow javadoc generation with javadoc 8

Should be removed after all javadoc comments are fixed.