Add 'digest_timeline' option to twitterlogger.

If true (default), use current behaviour (ie digest of all tweets since
last run). If false, creates a new DayOne entry per tweet.
Update README.md

Deleted typo and added Apple developer download link for command line tools.
Merge pull request #243 from larryhynes/patch-3

Update README.md
Merge pull request #223 from randomphrase/twitter-nodigest

Add 'digest_timeline' option to twitterlogger.