Private-in-file declarations conflict with public overload-equivalent declarations
in other files in the same package.
Move functions for grouping possible redeclarations to OverloadResolver
(since they are used only there).
Refactor redeclarations / conflicting overloads reporting.
- render the whole line where the error/warning points to, if any, and another
line with '^', like other compilers do
- lowercase diagnostic severity
- decapitalize the message if it doesn't start with a proper name
Kirill Rakhman