Release 0.1.15

* Fixed compilation warnings
* Fixed code quality issues found by CodeQL
* Upgraded base image from alpine:3.12.6 to alpine:3.12.7
  See CWE-125 and CVE-2021-30139). This is *not* a security issue if
  you just use the webdis image to run the service, but could be if
  you're building a new Docker image using webdis as a base image.

src/version.h

@@ -2,7 +2,7 @@
 #define VERSION_H
 
 #ifndef WEBDIS_VERSION
-#define WEBDIS_VERSION "0.1.15-dev"
+#define WEBDIS_VERSION "0.1.15"
 #endif
 
 #endif /* VERSION_H */