[API,FEATURE] added additional input and output type prefix to arg_parse.

Added two new ArgumentTypes, INPUTPREFIX and OUTPUTPREFIX. The user can now declare prefix
options/arguments which will be returned by the parser like a string option/argument but
indicate that more then one file with this shared prefix will be generated by the tool.
The user is responsible to make sure that all files he creates really share the prefix.
Note that no restriction checking is carried out while parsing. The supported format is
only an indicator for workflow engines like knime.
Merge pull request #3 from aiche/prefix-support

[API,FEATURE] added additional input and output type prefix to arg_parse