Fixed typo in mapping documentation

"Classthat" to "Class that" line #69
Merge pull request #777 from Blazinn/patch-2

Fixed typo in mapping documentation
Fixed typo in property mapping

Changed 'pecify' to 'specify' line # 246
Fixed grammar in custom data types

Changed 'are apply' to 'are applied'
Merge pull request #778 from Blazinn/patch-3

Fixed typo in property mapping
Merge pull request #779 from Blazinn/patch-4

Fixed grammar in custom data types