Bulgarian localisation

Start translation to Bulgarian language.
Update 02-Loading-a-Spreadsheet.md
Update 10-Reading-and-Writing.md
Check whether margin-left is set in excel file when reading
Merge pull request #220 from JackStone123/patch-2

Update 10-Reading-and-Writing.md
Merge pull request #219 from JackStone123/patch-1

Update 02-Loading-a-Spreadsheet.md
Merge pull request #221 from nendrew/develop

Check whether margin-left is set in excel file when reading
Merge pull request #216 from nickypn/patch-1

Bulgarian localisation