Make "createConverterToAvro" function public static

[ovj]

This will help createConverterToAvro being used outside of AvroOutputWriter.

[codecov-io]

Codecov Report

Merging #220 into master will decrease coverage by 0.43%.
The diff coverage is 96.07%.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
- Coverage    90.4%   89.96%   -0.44%     
==========================================
  Files           5        5              
  Lines         323      329       +6     
  Branches       49       52       +3     
==========================================
+ Hits          292      296       +4     
- Misses         31       33       +2

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[mnarrell]

Wouldn't it make sense to change the access modifiers on all these schema conversion functions? We have lots of AVRO encoded data that is not accessible via a filesystem path (stored in Redis/RDBMS/etc) that we'd love to transform into Dataframes and vice versa.