Merge branch 'BeyondMySouls-feature/fetch-sheet-names'

Update README.md

Add Saving event (fixes mganss#153)

Add support for Guid (fixes mganss#147)

Map subtypes only if not already mapped (see mganss#130)

Process nested type property only if no custom mapping (see mganss#130)

Deploy to GitHub releases

Update NPOI to 2.5.3

Fix comment

Remove unnecessary Ignore attribute