Add functionality to print the scientific type hierarchy

[ablaom]

After this PR:

julia> scitype()
Found
  Known
    Annotated
    AnnotationOf
    Compositional
    Finite
      Multiclass
      OrderedFactor
    Image
      ColorImage
      GrayImage
    Infinite
      Continuous
      Count
    ManifoldPoint
    Multiset
    ScientificTimeType
      ScientificDate
      ScientificDateTime
      ScientificTime
    Table
    Textual
  Unknown

Output can be diverted to an IO with scitype(io=...).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.30%. Comparing base (d2ffbbc) to head (4e24418).
⚠️ Report is 13 commits behind head on dev.

❌ Your project status has failed because you have indirect coverage changes. Learn more about Unexpected Coverage Changes and reasons for indirect coverage changes.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #30      +/-   ##
==========================================
- Coverage   93.93%   92.30%   -1.64%     
==========================================
  Files           2        2              
  Lines          33       39       +6     
==========================================
+ Hits           31       36       +5     
- Misses          2        3       +1     

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