Changed License to MIT

[MischaPanch]

We decided to change the license from GPL to the more permissive MIT, this makes it easier to use Serena in more projects, and also creates less friction when merging changes back to the MIT licensed multilspy.

@marcelomendoncasoares @shyraptor @HillLiu You have contributed some code under the GPL license. I suspect you don't mind the change to a more permissive one :), so this is mainly an FYI. But let me know if you do - in case you wish so, we could remove your commits.

[marcelomendoncasoares]

No objections on my end. This is really a welcome change!

[HillLiu]

I’m also really glad to see that Serena is moving in the direction of developing under an MIT license.