refactor changelog generator to use only api

[eritikass]

so there is no git checkout, all data should be available on github api. Also, commit should be done using github api.

one thing - if possible we should try to wrap github api with wrapper so we can easily replace it with gitlab or bitbucket.

/cc @litvand @OmIkRoNiXz

[litvand]

There is no danger of running out of API requests?

[eritikass]

https://developer.github.com/v3/#rate-limiting

For API requests using Basic Authentication or OAuth, you can make up to 5000 requests per hour. Authenticated requests are associated with the authenticated user, regardless of whether Basic Authentication or an OAuth token was used. This means that all OAuth applications authorized by a user share the same quota of 5000 requests per hour when they authenticate with different tokens owned by the same user.

Based for this I would say that we should be fine - we just need to keep track of users... don't think its that likely that some user is shared so heavily that he will end up using more than 5k time an hour.

and there is also api to check limits:

• https://api.github.com/rate_limit