Improve the documentation of Agda files involving Algorithmic part 1

[ramsay-t]

The files involved, the number of lines, and the estimated percentage of documentation completion (0 is no documentation at all, 100 is documentation is completed).

File | Number of lines | Percentage of documentation -- | -- | -- Algorithmic | 212 | 90% Algorithmic.RenamingSubstitution | 394 | 10% Algorithmic.Reduction | 279 | 0% Algorithmic.ReductionEC | 1568 | 0%