Improve error checks in Mimedir parser

[KristofferFM]

The Mimedir parser has a general flaw which is it simply ignores tokens it doesn't recognize.

As an example, the following property is invalid according to the specifications, and should be rejected by the parser.

FN;P1=value1; P2=value2:value

The problem is a whitespace in front of parameter name P2, which is not allowed according to the grammar described here . However, the current Mimedir parser do accept the line and furthermore misinterprets it to be on this format:

FN;P1=value1,value2:value

This pull request solves this specific problem by introducing the possibility to look back on the previous token parsed. Maybe it can be further improved by adding more checks. However a more general solution should possibly be preferred, I guess a complete rewrite of the parser could be the best solution.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.76%. Comparing base (778bb46) to head (688c165).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #727   +/-   ##
=========================================
  Coverage     98.76%   98.76%           
- Complexity     1875     1877    +2     
=========================================
  Files            71       71           
  Lines          5345     5353    +8     
=========================================
+ Hits           5279     5287    +8     
  Misses           66       66           

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