Restructure project layout and clean up test suite

Move sources to src/, header to inc/, and tests to tests/src/.
Update Makefiles and .gitignore for the new layout.

Refactor test harness: add crash-wrapper macros (_S_CRASH,
_S_CRASH_I, _S_CRASH_V, _S_CRASH_BUF) replacing 58 hand-written
wrappers, add shared _s_test_int_range helper eliminating duplicate
_s_test_func, add _S_RAND_ITERS constant, move srand() to main()
in all test binaries, and add Doxygen comments to test_utils.h.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/ft_tolower.c b/src/ft_tolower.c
new file mode 100644
index 0000000..52fbc94
--- /dev/null
+++ b/src/ft_tolower.c
@@ -0,0 +1,9 @@
+#include "libft.h"
+
+int
+ft_tolower (int c)
+{
+  if (c >= 'A' && c <= 'Z')
+    return (c + ('a' - 'A'));
+  return (c);
+}