Implement DateParser class

[seetohjinwei]

Fixes #35

[codecov-commenter]

Codecov Report

Merging #136 (5393f48) into master (98de953) will decrease coverage by 0.31%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #136      +/-   ##
============================================
- Coverage     68.46%   68.14%   -0.32%     
  Complexity      474      474              
============================================
  Files            87       88       +1     
  Lines          1538     1554      +16     
  Branches        178      177       -1     
============================================
+ Hits           1053     1059       +6     
- Misses          425      436      +11     
+ Partials         60       59       -1     

Impacted Files	Coverage Δ
src/main/java/taskbook/commons/core/Messages.java	0.00% <ø> (ø)
...rc/main/java/taskbook/logic/parser/DateParser.java	0.00% <0.00%> (ø)
...rc/main/java/taskbook/storage/JsonAdaptedTask.java	55.17% <0.00%> (+2.04%)	⬆️
src/main/java/taskbook/model/task/Task.java	59.52% <0.00%> (+8.09%)	⬆️

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[xiaobill8]

LGTM!

[dexter-sim]

lgtm