add pangram tests
add pangram tests

this commit adds 4 total tests

1 non-pangram to resolve #222 (comparison to "abc...")
2 pangram with underscores
3 pangram with numbers
4 non-pangram where missing letters are replaced by numbers

2 and 4 are designed to fail solutions that rely on counting
the number of word characters (which include numbers and underscore)

3 is intended to clarify that numbers are allowed in a pangram
and thus their mere presence in 4 is not the cause of a failure

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