Get rid of prefix-based log levels and migrate to explicit verbosity log levels

[lukstafi]

It is significant complexity in the implementation, too cumbersome to write, too distracting to read, and doesn't integrate well with projects as a logging mechanism. Instead of prefix-based, we will have discrete linear log levels 0=nothing, 1, ..., 9=everything with 1 being the default, numerical suffixes 1 to 9 e.g. %debug2_sexp, where %debug_sexp = %debug1_sexp, not only on entry points but on almost all extension points (where it makes sense), e.g. %log3_entry, %log4, etc. The actual log level of any output is the maximum of log levels indicated in the scope.