#3 Add release notes for PlayStore/ApkPure/iOS

[timobaehr]

Add release notes for iOS

For iOS, the release notes can be queried in a simple way.

Add release notes for ApkPure

ApkPure is HTML and release notes must be extracted via regular expression.

Google Play status

Google Play is HTML and release notes must be extracted via regular expression.

Refactoring

• At the moment, all the code of the library is in a single file. In the context of this pull request, a file was created for each subject (class/entity). I also added Api where PlayStoreApi, AppleStoreApi and ApkPureApi implements Api.
• AppCheckerResult used positional arguments. I changed this to named arguments as it is likely that you swap the string arguments.
• Tests was missing. This makes a lot of sense for working on HTML with regular expressions.