Updated dev guide, Implemented SetTagCommand

[coveralls]

Pull Request Test Coverage Report for Build 179

• 1 of 62 (1.61%) changed or added relevant lines in 6 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-1.5%) to 78.627%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/seedu/address/logic/parser/AddressBookParser.java	0	1	0.0%
src/main/java/seedu/address/logic/parser/MarkCommandParser.java	0	6	0.0%
src/main/java/seedu/address/logic/parser/SetTagCommandParser.java	0	10	0.0%
src/main/java/seedu/address/model/mark/Mark.java	0	15	0.0%
src/main/java/seedu/address/logic/commands/SetTagCommand.java	0	29	0.0%
<!--	Total:	1	62	1.61%	-->

Files with Coverage Reduction	New Missed Lines	%
src/main/java/seedu/address/logic/parser/MarkCommandParser.java	1	0.0%
<!--	Total:	1		-->

Totals
Change from base Build 177:	-1.5%
Covered Lines:	1832
Relevant Lines:	2330

---

💛 - Coveralls

[andrewtanJS]

looks good!