New features: (1) multicolumn section; (2) table width; (3) table row repeat as header & break across pages; (4) superscript & subscript font

Changes:
- Use constants instead of hardcoded name and size for font (Arial, 20)
- Section: Multicolumn (Sample_05_Multicolumn.php)
- Section: Different section break (Sample_05_Multicolumn.php)
- Paragraph: Hanging paragraph (no sample)
- Font: Superscript and subscript (Sample_04_Textrun.php)
- Table: Table width in percentage (no sample)
- Table: Repeat as header row (no sample)
- Table: Allow row to break across pages (no sample)