Implement outer product contractions

[mtfishman]

Fixes #13.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.17%. Comparing base (b876749) to head (7ae7c7d).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/blockedpermutation.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
- Coverage   92.54%   91.17%   -1.38%     
==========================================
  Files          16       16              
  Lines         322      340      +18     
==========================================
+ Hits          298      310      +12     
- Misses         24       30       +6     

Flag	Coverage Δ
docs	0.00% <0.00%> (ø)

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