Fixed ignored extra fields when logging exceptions

Various optimizations

Ensure sending thread is alive before appending log message

This reverts commit d41ceabe82. Which I suspect
does not work because the thread is stateful, i.e. after os.fork the thread in
copy of the process thinks it has already been started, even though it is not
alive. Probably safest to just get a new thread instance if a thread is not alive.

Also, only use lazy logger string formatting evaluations

* Use non-marked format holders since we only support 2.7+
* Use format holders, only, no concat

If you pass an empty list, tuple, False, 0, whatever.. it will assume th
token is valid, which it isn't.

Currently the module raises generic Exception (very "don't do it")

Manual draining

added a note that the type can't contain a space.

Add extra fields

rename setup.cfg.py to setup.cfg

Fix bug that consumed more logs while draining than Logz.io's bulk limit

Fix #7 Return formatted message if format string

Currently logging with:
```
logger.info('hello %s', 'world')
```
will send the string "hello %s" to logz.io instead of "hello world"

This commit fixes this situation.

Rewrite most of the handler, tests were introduced

Updated readme with the supported versions