Support PMCE on WebSockets

[jhoughjr]

This adds PMCE class to handle compression/decompression. A PR is pending in the vapor repo so it can be easily used inside of vapor.

[gwynne]

Good start, a couple notations

[codecov-commenter]

Codecov Report

Merging #145 (342c578) into main (a935b63) will decrease coverage by 26.82%.
Report is 1 commits behind head on main.
The diff coverage is 17.14%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #145       +/-   ##
===========================================
- Coverage   82.85%   56.03%   -26.82%     
===========================================
  Files           6        7        +1     
  Lines         659     1085      +426     
===========================================
+ Hits          546      608       +62     
- Misses        113      477      +364     

Files Changed	Coverage Δ
Sources/WebSocketKit/PMCE.swift	1.94% <1.94%> (ø)
Sources/WebSocketKit/WebSocket.swift	73.17% <40.69%> (-15.88%)	⬇️
Sources/WebSocketKit/WebSocketHandler.swift	58.02% <51.72%> (-4.48%)	⬇️
Sources/WebSocketKit/WebSocketClient.swift	90.67% <60.00%> (-4.68%)	⬇️
...urces/WebSocketKit/HTTPUpgradeRequestHandler.swift	73.77% <100.00%> (+1.84%)	⬆️

... and 1 file with indirect coverage changes

[jhoughjr]

Hummingbird will take flight as Vapor dissipates into nothingness.