make methods async via swig

[zoedberg]

Alternative to #6

With this PR we make methods async by changing the swig interface. We suppose the blocking version of the library is not needed, therefore we won't be keeping both versions (blocking and async) unless some users of this library will ask for this explicitly.

@tmalahie could you please check if this works good on your side? Also please note that most of rgb-lib methods should not be called in parallel. In the future we'll add some checks on the rust side to prevent parallel calls to "write" methods.

[tmalahie]

Hey sorry for the delay in response I was busy on other topics lately.
I like your suggestions of making everything async by default 👍 however I tested it and it doesn't seem to fix the main issue, even though it is async it is still making the main process freeze when I call an RGB function... I think the underlying library runs on the main thread which is what causes everything to hang despite the "asynceness"

[tmalahie]

Also please note that most of rgb-lib methods should not be called in parallel

For info in my PR I managed to solve this specific question of guaranteeing that everything is still called sequentially. The way it worked is that it only creates one background process for everything, and all the rgblib functions are called within this process. So when you call an rgb function, if there is a previous operation in progress it will wait for it to complete before running the next one.