add remove subcommand to remove the entry

[Songmu]

resolve #130

[coveralls]

Pull Request Test Coverage Report for Build 6747105730

Warning: This coverage report may be inaccurate.

We've detected an issue with your CI configuration that might affect the accuracy of this pull request's coverage report.
To ensure accuracy in future PRs, please see these guidelines.
A quick fix for this PR: rebase it; your next report should be accurate.

• 0 of 45 (0.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.5%) to 27.938%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
atom/client.go	0	4	0.0%
broker.go	0	6	0.0%
main.go	0	35	0.0%

Totals
Change from base Build 6705204831:	-1.5%
Covered Lines:	252
Relevant Lines:	902

---

💛 - Coveralls