Add mapping between differents headers names and fields object target

[xscorpio972]

Correction for issue #15

[mminella]

Unless I'm missing something the new annotation is available only at the method level, yet the mapping functionality for the non-annotation version works at the field level as well. Can we get this updated to support both?

[mdeinum]

This issue hasn't seen much attention. Next to that the same could be achieved (for the mapping) using a StaticColumnNameExtractor and skip the first row of the sheets/xls that is being read. With that I'm going to close this issue.