Update User Guide and Developer Guide for Tasks

[jiayushe]

• Fix a bug with adding new tasks
• Fix parseRemark and parseSource
• Fix incorrect prompt for add command and edit command
• Fix hashCode and toString for Problems
• Update User Guide
• Update Developer Guide
  ==========
• Fix Implement parse methods #39
• Fix Incorrect command prompt for AddCommand #55
• Fix Hashcode for Problem doesn't include difficulty. #60

[le0tan]

lgtm

[coveralls]

Pull Request Test Coverage Report for Build 168

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 211 unchanged lines in 13 files lost coverage.
• Overall coverage increased (+0.2%) to 37.706%

---

Files with Coverage Reduction	New Missed Lines	%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/HelpCommand.java	1	0.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/AddCommand.java	3	75.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/FindPlanCommand.java	4	0.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/AddPlanCommand.java	7	0.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/AddTaskCommand.java	7	48.28%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/SortCommand.java	7	89.06%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/DeleteTaskCommand.java	9	0.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/DoneTaskCommand.java	9	0.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/commands/UndoneTaskCommand.java	9	0.0%
file:/home/travis/build/AY1920S1-CS2103T-W11-1/main/src/main/java/seedu/algobase/logic/parser/ParserUtil.java	20	36.11%

Totals
Change from base Build 163:	0.2%
Covered Lines:	868
Relevant Lines:	2302

---

💛 - Coveralls