Support multi-named keywords without underscore

[ulmer-a]

Closes #207

Support multi-named keywords and log a diagnostic when encountered. The user should be encouraged to use the underscore variants by an error message similar to "found ENDFUNCTIONBLOCK, consider using END_FUNCTION_BLOCK instead".

[codecov]

Codecov Report

Merging #213 (1ef7314) into master (ed845d6) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #213      +/-   ##
==========================================
+ Coverage   96.70%   96.76%   +0.05%     
==========================================
  Files          41       41              
  Lines       15392    15430      +38     
==========================================
+ Hits        14885    14931      +46     
+ Misses        507      499       -8     

Impacted Files	Coverage Δ
src/lexer.rs	95.32% <100.00%> (+0.38%)	⬆️
src/lexer/tests/lexer_tests.rs	98.60% <100.00%> (+0.07%)	⬆️
src/lib.rs	89.68% <100.00%> (+3.17%)	⬆️

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[ulmer-a]

@riederm @ghaith I feel like there should be a better way to do this... However, if you haven't got any tips, this would be my approach. Actually now I think it's not event that bad...

The codecov/patch fails, because the added #[token(...)] lines. I'm not sure how to deal with this, since I already wrote a test that should cover them... recent PR fixed this

[riederm]

I think it's good 👍