Rename and deprecated rfc8888 package

[mengelbart]

Rename rfc8888 packages. We don't have any other packages named after the respective RFCs.

[codecov]

Codecov Report

❌ Patch coverage is 7.14286% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.56%. Comparing base (3cb438f) to head (7f82d87).

Files with missing lines	Patch %	Lines
pkg/rfc8888/rfc8888.go	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #351      +/-   ##
==========================================
- Coverage   78.64%   78.56%   -0.09%     
==========================================
  Files          82       83       +1     
  Lines        5113     5126      +13     
==========================================
+ Hits         4021     4027       +6     
- Misses        921      930       +9     
+ Partials      171      169       -2     

Flag	Coverage Δ
go	78.56% <7.14%> (-0.09%)	⬇️
wasm	75.92% <7.14%> (-0.20%)	⬇️

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