make annotations available in codegen

[riederm]

we dropped the idea of importing everything into one big
compilation unit. instead we now do multiple calls to the
generator - one for every parsed compilation unit.

[codecov]

Codecov Report

Merging #251 (6a75b9b) into master (ebf1b8f) will decrease coverage by 0.00%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master     #251      +/-   ##
==========================================
- Coverage   95.20%   95.19%   -0.01%     
==========================================
  Files          39       39              
  Lines       10543    10546       +3     
==========================================
+ Hits        10037    10039       +2     
- Misses        506      507       +1     

Impacted Files	Coverage Δ
src/resolver.rs	95.75% <0.00%> (+0.88%)	⬆️
src/codegen.rs	100.00% <100.00%> (ø)
src/lib.rs	95.91% <100.00%> (-0.02%)	⬇️
src/ast.rs	89.87% <0.00%> (-1.09%)	⬇️
src/typesystem.rs	96.18% <0.00%> (+0.27%)	⬆️

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