Mockk junit5

[FredDeschenes]

As mentioned in #23.
Take a good look at the build.gradle file please, I couldn't get Jacoco to run locally and there's probably a way to only use mockk-dsl but I couldn't get it to work.

[codecov-io]

Codecov Report

Merging #34 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #34   +/-   ##
=========================================
  Coverage     80.36%   80.36%           
  Complexity      516      516           
=========================================
  Files            62       62           
  Lines          1375     1375           
  Branches        220      220           
=========================================
  Hits           1105     1105           
  Misses          173      173           
  Partials         97       97

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[oleksiyp]

I merged and edited few things:

• embedded it to main mockk sub-project
• added auto registration (don't know if it works with most recent version of JUnit5, because information was removed from docs)
• minor refactoring
  Released as v1.7.8