first cut at redis support

[memory]

• add a redis store implementing stores.Storage
• add config file support to pick a storage backend
• add config file support to set redis host:port and password

Also:

• add docker_releases to .gitignore

[coveralls]

Pull Request Test Coverage Report for Build 347

• 6 of 265 (2.26%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-11.6%) to 37.905%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
stores/store.go	6	11	54.55%
stores/redis/redis.go	0	254	0.0%
<!--	Total:	6	265	2.26%	-->

Totals
Change from base Build 290:	-11.6%
Covered Lines:	409
Relevant Lines:	1079

---

💛 - Coveralls

[mxschmitt]

And thanks for you PR 👍

[memory]

Okay, the second commit in this PR should address the style concerns. Also I updated the README and the example config.yaml.

[mxschmitt]

As a final step please fix your comment styling to "MethodName ..." https://app.codacy.com/app/maxibanki/golang-url-shortener/pullRequest?prid=1621352

[memory]

55311f5 updates the comment styling to sentence format as requested.