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.