* Refactor readers to get a proper DI
Similar to what was done with writers, readers also needed to be updated to match the new way of doing things.
This commits promotes a better DI (factories, injection through constructors).
* Escapers should not be singletons
Instead, they should be proper object that can be injected where needed.
- To determine if a style should apply a date format, the presence of "applyNumberFormat" attribute on the "cellXfs" section of styles.xml is now optional. We only look at the "numFmtId" attribute (but early return if "applyNumberFormat" is set to "0").
- The format code can contain lowercase AND now uppercase characters as its pattern.
- "General" format code used as a custom format is now supported. It seems to be used by a bunch of programs...
Although Excel has a Date type, older Excel versions use numeric values to store dates.
The value represents the number of days since Jan 1st, 1900.
The only way to tell if the value is a number or a date is to look at the styles.xml and check if the cell has date formatting.
