Don't lowercase section title IDs in parser

[DavidGamba]

Defer lowercase to templates instead

Fixes #1063

[codecov[bot]]

Codecov Report

Merging #1100 (574ec8b) into master (b92f431) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1100   +/-   ##
=======================================
  Coverage   80.79%   80.79%           
=======================================
  Files          89       89           
  Lines        7587     7588    +1     
=======================================
+ Hits         6130     6131    +1     
  Misses        963      963           
  Partials      494      494           

[xcoulon]

Thanks for this PR, @DavidGamba!