0.3.0 Release attempt 2

[0Hughman0]

• Sure up little changes to ipygui.
• Update docs, including migration guide.
• ... get to work on the jl_gui.

[codecov]

Codecov Report

Attention: Patch coverage is 95.48387% with 7 lines in your changes missing coverage. Please review.

Project coverage is 83.48%. Comparing base (f260ae0) to head (95fa09d).
Report is 3 commits behind head on 0.3.x.

Files	Patch %	Lines
cassini/migrate/__main__.py	89.28%	3 Missing ⚠️
cassini/migrate/base.py	87.50%	3 Missing ⚠️
cassini/sharing.py	96.87%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##            0.3.x     #152       +/-   ##
===========================================
+ Coverage   67.85%   83.48%   +15.63%     
===========================================
  Files          21       23        +2     
  Lines        1683     1726       +43     
===========================================
+ Hits         1142     1441      +299     
+ Misses        541      285      -256     

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[0Hughman0]

You should really double check the changes made to InputSequence are fine in other places it's used...