Split into multiple files

For multiple reasons the program is now split:
- Make future porting to OpenBSD easier
- Assign header includes to individiual functions
- Make future program extensions easier
- Recompile only changed parts

util.h

@@ -0,0 +1,6 @@
+static char buf[1024];
+
+#define LEN(x) (sizeof (x) / sizeof *(x))
+
+const char *bprintf(const char *fmt, ...);
+int pscanf(const char *path, const char *fmt, ...);