isogram: Revise canonical test data (#433)
isogram: Revise canonical test data (#433)

* isogram: Remove non-ASCII test cases

* isogram: Add test case descriptions

* isogram: Remove autological description

* isogram: Change misleading test case input

Vankog/problem-specifications,petertseng/x-common,ErikSchierboom/x-common,exercism/x-common,jmluy/x-common,exercism/x-common,rpottsoh/x-common,jmluy/x-common,kgengler/x-common,kgengler/x-common,rpottsoh/x-common,petertseng/x-common,Vankog/problem-specifications,ErikSchierboom/x-common,jmluy/x-common