Code refactor: Add prefix "XlsxFormat" to some internal class
Code refactor: Make use of QSharedDataPointer for Format
Code refactor: numFmt part of QXlsx::Format
Code refactor: Remove private class XlsxFormatFontData
Code refactor: Remove private class XlsxFormatBorderData
Code refactor: Remove private class XlsxFormatFillData
Code refactor: Remove private class XlsxFormatAlignmentData and
XlsxFormatProtectionData
RichString: Using Format instead of Format *
API change: Using Format instead of Format *
Code refactor: Only create FormatPrivate when needed.
Update to Version 0.2.0
Make RichString public
Format: Use QMap instead of QHash

As the items of QHash are arbitrarily ordered, so the same formats may generate
different formatKey
Update documentation