Read the ROSCONSOLE_FORMAT env var to format the logs

[romainreignier]

This is a naive approach, not much optimized because each call to String::replace() will allocate a new String, a bit like the rospy implementation.

I did not implement the tokens for which the value were not already available. This can be done later.

The new thread-id dependency should not bring too much new dependencies as it only requires libc on Linux for example.

I have added a space to INFO and WARN level strings so all levels have the same string length.
I did this to mimic rosconsole.
But I have just noticed that on the noetic-devel branch, not yet released, the spaces are gone thanks to this PR ros/rosconsole#52
I personally prefer the space so the logs are well aligned.

To implement several loggers, we would need a more advanced logging system. Did you try to use the existing rust log ecosystem and create a rosrust backend for it?

[romainreignier]

Note that I did not add test because I do not know how to capture stdout in the tests.
We would need to use write!() to an object that would be stdout by default but a buffer for the tests.