Execute in the CI the build commands from readme files

[limdor]

For each example there are several build commands that we want to show to the user. To make sure that these build commands are working all the time, they are executed in the CI adding them in the appveyor file.
The problem with this approach is that the commands are repeated, appearing once in the appveyor file and once in the Readme file.
The goal of this task is to have a script that parse the readme files to find bazel commands and these commands are executed in the CI.