Implement Functions in CQL

[alexanderkiel]

Closes: #501

[codecov]

Codecov Report

Merging #766 (579f233) into develop (cd22ea8) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #766      +/-   ##
===========================================
+ Coverage    93.64%   93.70%   +0.05%     
===========================================
  Files          233      234       +1     
  Lines        14387    14426      +39     
  Branches       390      390              
===========================================
+ Hits         13473    13518      +45     
+ Misses         524      518       -6     
  Partials       390      390              

Impacted Files	Coverage Δ
modules/cql/src/blaze/elm/compiler/core.clj	88.67% <ø> (ø)
...dules/cql/src/blaze/elm/compiler/external_data.clj	77.19% <100.00%> (+0.61%)	⬆️
modules/cql/src/blaze/elm/compiler/function.clj	100.00% <100.00%> (ø)
modules/cql/src/blaze/elm/compiler/library.clj	98.21% <100.00%> (+0.53%)	⬆️
modules/cql/src/blaze/elm/compiler/queries.clj	74.87% <100.00%> (ø)
...dules/cql/src/blaze/elm/compiler/reusing_logic.clj	82.97% <100.00%> (+5.05%)	⬆️
modules/cql/src/blaze/elm/deps_infer.clj	79.23% <0.00%> (+1.73%)	⬆️