functions mock feature

[kwolfy]

I propose to add the ability to mock functions

issue #101

[codecov-io]

Codecov Report

Merging #102 into master will increase coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
+ Coverage   94.89%   94.99%   +0.09%     
==========================================
  Files          34       34              
  Lines         607      619      +12     
  Branches       69       69              
==========================================
+ Hits          576      588      +12     
  Misses         22       22              
  Partials        9        9

Impacted Files	Coverage Δ
src/ts-mockito.ts	97.26% <100%> (+0.53%)	⬆️

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[gcaggia]

Why this PR is not accepted and merged @NagRock?
I need that for my current project.