Documentation/units not in brackets

[PhRosenberger]

Reference to a related issue in the repository

This PR solves #362 as unit-writing is now corrected.

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Corrects writing of units without brackets in whole docu.

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@jdsika could you please double-check?

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• My code and comments follow the style guidelines and contributors guidelines of this project.
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests / travis ci pass locally with my changes.

[jdsika]

LGTM

[jdsika]

@vkresch could we add a test for this?

[vkresch]

@jdsika yes we could define all available units in a list and then check for each found unit if brackets exist. If a unit is found and no brackets around it are detected (or detect just white space) the test passes. Not sure how big of a task would be defining the list. Maybe we just define for now all available units in OSI and add them later on as we go. Something like this:
['m', 'm/s', 'Pa', 'bar', ...]

[jdsika]

I will merge for now and we may add the tests later - let it sink in a little bit