Disable log file *initially* when using ELPP_NO_LOG_TO_FILE, to be consistent with documentation

[rggjan]

Currently, setting "ELPP_NO_LOG_TO_FILE" disables logging to file entirely. However, the documentation says it is only disabled initially.

When applying the current pull request, it is possible to disable it initially and set a custom log file location at runtime like this:

#define ELPP_NO_LOG_TO_FILE
#define ELPP_NO_DEFAULT_LOG_FILE

#include <easylogging++.h>

INITIALIZE_EASYLOGGINGPP

int main(int, char **) {
  el::Loggers::reconfigureAllLoggers(el::ConfigurationType::Filename,
                                     "test.log");
  el::Loggers::reconfigureAllLoggers(el::ConfigurationType::ToFile, "true");

  LOG(INFO) << "Test";
}

This is impossible with the current implementation.

This is a

• Breaking change
• New feature
• [ x] Bugfix

[abumq]

Please make all the changes to develop branch

[abumq]

I have applied this change manually in fb67e3a