Add LGTM code quality badges

[xcorail]

Hi there!

I thought you might be interested in adding these code quality badges to your project. They will indicate a very high code quality to potential users and contributors.
To get an idea of the analyses reflected by these grades, check the alerts discovered by LGTM.

N.B.: I am on the team behind LGTM.com, I'd appreciate your feedback on this initiative, whether you're interested or not, if you find time to drop me a line. Thanks.

[xcorail]

Hello @Siemienik

Happy you found it useful.
A few precisions on the runs:

• Currently, LGTM polls your repo once a day, and analyzes all new commits, most recent first
• We recommend to activate Automated Code Review. This way LGTM analyzes your Pull Requests immediately and report any new problem directly in the comments. It's free, and it's a one click operation

For support, questions, feedback: https://discuss.lgtm.com/
Cheers