Fix tree-shaking of the SDK

[thornbill]

• Refactor getters for API classes to individual utility functions to allow for tree shaking.
• Add list of breaking changes in next release.

Fixes #137

[codecov-commenter]

Codecov Report

Merging #149 (8543500) into master (1a69409) will increase coverage by 2.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
+ Coverage   83.56%   85.71%   +2.14%     
==========================================
  Files          17       77      +60     
  Lines         426      490      +64     
  Branches       44       44              
==========================================
+ Hits          356      420      +64     
  Misses         70       70              

Impacted Files	Coverage Δ
src/index.ts	100.00% <ø> (ø)
src/models/recommended-server-info.ts	100.00% <ø> (ø)
src/api.ts	100.00% <100.00%> (ø)
src/discovery/recommended-server-discovery.ts	100.00% <100.00%> (ø)
src/utils/api/activity-log-api.ts	100.00% <100.00%> (ø)
src/utils/api/api-key-api.ts	100.00% <100.00%> (ø)
src/utils/api/artists-api.ts	100.00% <100.00%> (ø)
src/utils/api/audio-api.ts	100.00% <100.00%> (ø)
src/utils/api/branding-api.ts	100.00% <100.00%> (ø)
src/utils/api/channels-api.ts	100.00% <100.00%> (ø)
... and 55 more

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