Refactor client.today and client.yesterday

[noriapi]

Since most parts of client.today and client.yesterday are the same code, i extracted it as client._daily.

[noriapi]

Sorry, I don't know how the refactoring should be described in keep a changelog.

[epwalsh]

Thanks @noriapi, this is great. For the CHANGELOG, I would just add something like this:

### Changed

- (internal) Refactored daily note creation

[noriapi]

Thanks @noriapi, this is great. For the CHANGELOG, I would just add something like this:

### Changed

- (internal) Refactored daily note creation

Thank you, I added it to CHANGELOG.

[epwalsh]

LGTM. Thanks @noriapi :)