Move all core-functionality to subsurface-core

And adapt a new CMakeLists.txt file for it. On the way I've also
found out that we where double-compilling a few files. I've also
set the subsurface-core as a include_path but that was just to
reduce the noise on this commit, since I plan to remove it from
the include path to make it obligatory to specify something like

 include "subsurface-core/dive.h"

for the header files. Since the app is growing quite a bit we ended
up having a few different files with almost same name that did
similar things, I want to kill that (for instance Dive.h, dive.h,
PrintDive.h and such).

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

subsurface-core/version.h

@@ -0,0 +1,16 @@
+#ifndef VERSION_H
+#define VERSION_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+const char *subsurface_version(void);
+const char *subsurface_git_version(void);
+const char *subsurface_canonical_version(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif