Description:
------------
This request is for generic logging capabilities in PhD. For example, let's say we want to log every function that lacks version information (when a function is available in PHP/PECL, via versions.xml, via functable.php) then currently we might define $missingVersions and add this to phpdotnet.php:

  if (!isset($this->versions[$funcname])) {
    self::$missingVersions[] = $funcname;
  }

And in build.php:

  print_r(array_unique(phpdotnet::$missingVersions));

Rather, it would be nice to instead officially log such information in one place so instead of some variable, something like:

  if (!isset($this->versions[$funcname])) {
    log_errors('missing_versions', $funcname);
  }

Then have a single place to categorically output all such logged errors. We'd also log missing mappers, missing translated text, etc.