.gitignore: ignore local config.xml in working directory
Book: indentation cosmetics for static constants
Book.writeConfig: throw undeclared RuntimeExceptions like readConfig
Book.writeConfig: add debugMode parameter like in readConfig
Book: write character encoding iso-8859-15 to config.xml

This simplifies reading the config file from the input stream because
Xstream will respect the encoding found at the beginning of the stream.

Attention: XStream still writes its output in with UNIX line breaks
witout regard of the Java system property 'line.separator'. This is
kinda strange, but okay as long as GOC users do try to edit the config
file with a bad editor like Windows Notepad.
Options: add "-w|--write-config" for writing config.xml

This is an easy way for JAR users to extract the embedded default
config.xml to disk and edit it subsequently, e.g. in order to add new
books not contained in the upstream version. This way they do not have
to wait for me to update the Git repo and the downloadable JAR.

User self-service. :-) Refers to #5.