Massive amount of logging in output.xml

[Lakitna]

When running keywords asynchronously, a lot more output is written to output.xml.

I ran the same (decently complex) code async and sync.

Note: The comparison between the sync and async ones is far from perfect. The async versions error due to #95.

For the second one, I uncommented these lines:

robotframework-gevent/src/GeventLibrary/keywords/gevent_keywords.py

Lines 54 to 55 in a1676ca

	ctx.output.start_keyword = lambda kw: _start_keyword(kw, built_in)
	ctx.output.end_keyword = lambda kw: _end_keyword(kw, built_in)

	output.xml size
async (with gevent)	4775KB
async (with gevent, removed monkey-patched log changes)	314KB
sync	646KB

That makes the async version over 7 times as big. For me, that is not workable as writing to output.xml has become a performance bottleneck in my setup.

When removing the monkey-patched logging there is a lot less logging. It makes it hard to debug, but fast to run.

It'd be great if the logging could be reduced significantly. Alternatively, it can take inspiration from the robot:flatten tag and give the user control over how much is logged.