Started development on version 0.9.3

- Updated the README instalation instructions and added a new section
  in the change log
Changed version in pom files.
Merge branch 'master' into version-0.9.3

Conflicts: (keeping version-0.9.3)
	README.org
	bte-core/pom.xml
	bte-io/pom.xml
	pom.xml
Added ExcelDataLoader and MultiSourceDataLoader
Bugfix commit

- CSVOutputGenerator does not result in NullPointerException if the
  requested field in the Record does not exist.

- Changed the result type of getPrefixes from Iterator to Iterator<String>
  and eliminated a warning.
Change the ExcelDataLoader to use the apache poi API instead of jxl
Fixed a bug in the ExcelDataLoader

The ExcelDataLoader can now handle simlpe cell types, and specifically
string, numeric and date. Previously it tried to read everything as
string and if the cell was of another type, it would throw an
exception.
Install javadocs and sources in local repository

When mvn install is issued, the sources and the javadocs will be
installed in the local repository. This should help integrating with
IDEs like eclipse.
Added license notices to ExcelDataLoader and MultiSourceDataLoader
Add the entries in the changelog