Add slvs prebuilt for Python3

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "py_slvs_mac"]
 	path = py_slvs_mac
 	url = https://github.com/realthunder/py_slvs_mac.git
+[submodule "py3_slvs"]
+	path = py3_slvs
+	url = https://github.com/realthunder/py3_slvs.git

py3_slvs

@@ -0,0 +1 @@
+Subproject commit 30f34766bbdf129536e682f1dcb302f5ac06c81c

sys_slvs.py

@@ -1,14 +1,19 @@
 from .deps import with_metaclass
 from .system import System, SystemBase, SystemExtension
 from .utils import syslogger as logger, objName
-import platform
+import platform, sys
 
-if platform.system() == 'Darwin':
-    from .py_slvs_mac import slvs
-else:
-    try:
-        from py_slvs import slvs
-    except ImportError:
+try:
+    from py_slvs import slvs
+except ImportError:
+    if platform.system() == 'Darwin':
+        if sys.version_info[0] == 3:
+            from .py3_slvs_mac import slvs
+        else:
+            from .py_slvs_mac import slvs
+    elif sys.version_info[0] == 3:
+        from .py3_slvs import slvs
+    else:
         from .py_slvs import slvs
 
 class SystemSlvs(with_metaclass(System, SystemBase)):