lex_test.go: Rewrite TestIsLastLine()
lex_test.go: Reorder functions
lex_test.go: Change nIndex 1 to 0 in lexerTests
lex.go: Add debug output in newLexer()
lex.go: Redo next() debug output
lex.go: Refactor for split line input

The code is much cleaner now that input is split into lines before lexing.
Fix startPosition in remaining section tests
Test coverage 100%