Add BLE ad data generation method

[shreyasminocha]

Resolves #100

[!NOTE] Please consider squashing and replacing the commit message.

[malmeloo]

I appreciate the effort, but I'm not sure if this is the right approach to implementing it. The library already contains code to extract the public key from broadcast data (see the scanner code), and it would probably make sense to implement the reverse operation in the library as well. A method in the HasPublicKey class would probably suffice.

[malmeloo]

Looks good, but now the example is missing 😄. Do you want to add it or should I merge and add it myself?

[shreyasminocha]

Ah, I misunderstood your last comment. I can add the example!

[malmeloo]

I've made some tiny changes for the sake of flexibility and method naming consistency. I think it should be trivial enough so an example might not be necessary, but we can always add one later. Thanks again!