[Tolk] Completely rework stdlib: multiple files and renaming

- split stdlib.tolk into multiple files (tolk-stdlib/ folder)
  (the "core" common.tolk is auto-imported, the rest are
  needed to be explicitly imported like "@stdlib/tvm-dicts.tolk")
- all functions were renamed to long and clear names
- new naming is camelCase

tolk/compiler-state.h

@@ -52,10 +52,9 @@ struct CompilerSettings {
   int optimization_level = 2;
   bool stack_layout_comments = true;
 
-  std::string entrypoint_filename;
   std::string output_filename;
   std::string boc_output_filename;
-  std::string stdlib_filename;
+  std::string stdlib_folder;    // a path to tolk-stdlib/; files imported via @stdlib/xxx are there
 
   FsReadCallback read_callback;
 
@@ -82,8 +81,6 @@ struct CompilerState {
   std::vector<SymDef*> all_code_functions, all_global_vars, all_get_methods, all_constants;
   AllRegisteredSrcFiles all_src_files;
 
-  std::string generated_from;
-
   bool is_verbosity(int gt_eq) const { return settings.verbosity >= gt_eq; }
 };