FESpace consistent assembly strategy

[JordiManyer]

• Add documentation on assembly strategies
• Add a new assembly strategy that works like FullyAssembledRows but doe not optimize column PRanges.

[codecov-commenter]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (3c2245c) 0.00% compared to head (0bcc8d9) 0.00%.
Report is 4 commits behind head on master.

Files	Patch %	Lines
src/Algebra.jl	0.00%	14 Missing ⚠️

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Additional details and impacted files

@@          Coverage Diff           @@
##           master    #134   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files          12      12           
  Lines        2448    2462   +14     
======================================
- Misses       2448    2462   +14     

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