v0.4.3: implement the following:
    fix issue #42
v0.4.2: implement the following:
    - fix issue #32
v0.4.1: implement the following:
    - use numpy.where to replace null_values and sd_values #30
v0.4.0: implement the following:
    - Python 3.9
    - fix issue #26
    - parsing of multilingual metadata
v0.3.4: implement the following:
    - fix issue #4
    - add 'get_codes' function
    - fix flake8 errors and warnings
v0.3.3: fix issue #8
v0.3.2: fix issue #5
v0.3.1: fix parsed values with semicolons
v0.3.0: implement the following:
    - remove leading and trailing blanks from element names (metadata_split_to_dict)
    - upgrade dependencies version
    - add dev packages
    - refactor unit and integration tests
v0.2.0: added support for null and statistical disclosure representation.