Major changes

• Drop support for non C++11 applications for major performance improvements
• Support for asyncrounous logging
• Major performance improvements
• Unhandled exception and crash logging (with optional stack trace)

This is not small change so will take quite some time to finish this so cant set due date just yet. First we will need to come up with proper design that is efficient, fast and can be relied upon.

For further details look at https://github.com/easylogging/easyloggingpp/issues?milestone=7&page=1&state=open and https://github.com/easylogging/easyloggingpp/issues?milestone=7&page=1&state=closed