v0.7.1: rename C core header to victronble_core.h (fixes #2)

src/ held both VictronBLE.h and victronble.h. On case-insensitive
filesystems (Windows, macOS) extracting the library ZIP overwrote one
with the other and the Arduino build failed.

The core header is now victronble_core.h in include/ and src/, and every
include is updated. include/victronble.h stays as a deprecated forwarder
so 0.7.0 Zephyr and host code still builds; it is never in src/.

check_version.sh now fails if two tracked paths differ only in case.

tests/vectors/test_main.c

@@ -12,7 +12,7 @@
 #include <string.h>
 #include <math.h>
 
-#include "victronble.h"
+#include "victronble_core.h"
 #include "test_vectors.h"
 
 static int failures;