Developer Friendly API Implementation

[tonyqus]

2.8.0

• Implement ISheet.Cells[] and ISheet.Rows[] #1695
• Developer Friendly Api Implementation I #1776
• Add ForceFormulaRecalculation method for IWorkbook #1817

[tonyqus]

@mganss I'm improving NPOI's API. A few API improvement will be shipped with NPOI 2.8.0.

Also there are a few performance improvement in NPOI 2.8.0. You can read the release note

If you have time, you can check which API can be used in ExcelMapper