Add unittests for the base class Operation. The tests focus on the static
factory method. This method has already been implemented.

Implement all parsing methods for Markdown syntax, such that all test
requirements are satisfied.

The commit provides a functioning CI and therefore closes #1.

Adds unittests for DoxecSyntax subclass Markdown. The implementation of these
tests lead to slight modifications in the doxec package. The DoxecSyntax.parse
expects a list of lines, which is modified in place, instead of a plain string.

Create an empty package named doxec.tests to store all unittests.

Fix mistakes indicated by previous pipeline. The errors arise from missing
imports or plain syntax errors.

Add gitlab-ci configuration using the attached docker image using ubuntu 16 and
python3. The CI consists of two test jobs: unittest and doctest

Add the `.gitignore` file containing wildcards for temporary vim files and the
python cache directory.

Adds skeleton classes for dexec package. Most classes define only a list of
methods, without implementation, but a short comment about its purpose. As of
now, the list of classes and methods, seems to be sufficient. The package lacks
unittests and the CI setup.