Implicitly split parameters through add_param, corrected encode events to support empty iterator input

[MattiasFredriksson]

Changes:

• GroupEditable.add_param(..) will now split the input into multiple parameters following the Name, Name2, Name3 standard if the leading dimension is to large (more then 255 entries).
• encode_event() should now accept an empty iterator without a missing reference which should fix UnboundLocalError: local variable 'i' referenced before assignment when shallow copying a c3d file with no events #48
• Added tests for writing files and corrected/improved/simplified related functions. This should provide some examples of writing files Not clear how to write a file #49 until documentation gets resolved.
• Some comments and new exceptions for bad inputs.

Notes:

• Separated changes to follow PEP standard and .format() rules in a separate branch as it became a distraction from the other changes.
• Writing parameters is slightly confusing, input expects Fortran format while reading returns data in C format. I have no intention to fix this until the remaining changes and documentation is merged.
• Implicitly splitting parameters is slightly problematic since there is no function for reading them as a single parameter (e.g. see More POINT:LABELS #47 ).

[Peaj]

Is there any reason this has not been merged yet? Works perfectly for me fixing the issue with c3d files using more than 255 labels.