Create interface for file data

[Syfaro]

This reworks the library's file handling to use a new interface for file data instead of relying on magic types and interfaces. This should also allow for users to implement the same methods for arbitrary external types to make uploads easier.

It introduces one breaking change (as far as I know) where strings to local file paths are no longer allowed.

[codecov]

Codecov Report

Merging #469 (d2539d0) into develop (309d612) will decrease coverage by 0.48%.
The diff coverage is 48.27%.

@@             Coverage Diff             @@
##           develop     #469      +/-   ##
===========================================
- Coverage    49.10%   48.62%   -0.49%     
===========================================
  Files            7        7              
  Lines         1507     1487      -20     
===========================================
- Hits           740      723      -17     
+ Misses         716      706      -10     
- Partials        51       58       +7     

Impacted Files	Coverage Δ
helpers.go	58.20% <ø> (ø)
types.go	75.92% <ø> (ø)
bot.go	39.46% <46.15%> (-0.91%)	⬇️
configs.go	43.60% <48.64%> (-0.96%)	⬇️

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