Add .gitattributes and normalize a few stray file's line endings

.gitattributes

+# test files have a mix of lf/crlf, and that's a good thing, for testing, don't mess with it
+# bash scripts need lines ending with lf, and that's correct for Windows too, e.g., under Cygwin
+# (scripts often don't have a suffix)
+* -text
+*.sh text eof=lf
+
+# txt files should be native and normalized
+*.txt text
+
+# source code can be native and normalized, but simpler if lf everywhere; will try that way
+*.h text eof=lf
+*.c text eof=lf
+*.cpp text eof=lf
+*.y text eof=lf