Implement Stats command

[moyj01]

No description provided.

[codecov-io]

Codecov Report

Merging #106 into master will increase coverage by 0.43%.
The diff coverage is 79.48%.

@@             Coverage Diff              @@
##             master     #106      +/-   ##
============================================
+ Coverage     61.44%   61.87%   +0.43%     
- Complexity      536      547      +11     
============================================
  Files           104      106       +2     
  Lines          1953     1991      +38     
  Branches        224      227       +3     
============================================
+ Hits           1200     1232      +32     
- Misses          668      674       +6     
  Partials         85       85              

Impacted Files	Coverage Δ	Complexity Δ
...du/flashcard/logic/parser/FlashcardDeckParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
src/main/java/seedu/flashcard/ui/MainWindow.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
.../seedu/flashcard/logic/commands/CommandResult.java	62.74% <70.58%> (+6.86%)	13.00 <1.00> (+1.00)
...a/seedu/flashcard/logic/commands/StatsCommand.java	100.00% <100.00%> (ø)	8.00 <8.00> (?)
...edu/flashcard/logic/parser/StatsCommandParser.java	100.00% <100.00%> (ø)	2.00 <2.00> (?)

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[tan-zhuoyao]

Please refer to my 1 comment, thank you!

[sgn00]

Fix the change