Smaller memory imprint of semicompiled code

[GillesDuvert]

Important evolution of previous PR #1681
It was found

1. that the memory imprint of the semi-compiled code could be made much smaller, and
2. that the size of save,/routine files that contained pro/fun issued from files with a large number of entries (e.g., atv.pro that contains all related routines needed) would erroneously duplicated many times the semi-compiled code.
   With the present setup, the size of the save file is approx twice the size of the corresponding .pro file, and the memory imprint negligible.

[codecov]

Codecov Report

Attention: 83 lines in your changes are missing coverage. Please review.

Comparison is base (7742324) 41.95% compared to head (d746672) 41.96%.

Files	Patch %	Lines
src/saverestore.cpp	60.54%	73 Missing ⚠️
src/dpro.cpp	87.30%	8 Missing ⚠️
src/gdlhelp.cpp	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1687      +/-   ##
==========================================
+ Coverage   41.95%   41.96%   +0.01%     
==========================================
  Files         356      356              
  Lines       95597    95606       +9     
  Branches    19662    19656       -6     
==========================================
+ Hits        40103    40123      +20     
+ Misses      55494    55483      -11     

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