Log Message:
libodfgen: Update to 0.1.7

libodfgen 0.1.7
- All:
    + switch to C++-11
    + fuzzing: correct many problem
    + support more text's style attributes
    + add support for named's graphic style
    + ods/odt: try to retrieve some MathML equations
- Chart:
    + support more attributes,
- Spreadsheet:
    + allow external file reference
    + do not create invalid file if there is more than 26*26 columns
- Other improvements and fixes.