Arithmetic Modules(#112)

[devRD]

*Added Arithmetic Modules' functions

*Added Arithmetic modules in index and readme

*Added Unit Tests of Arithmetic Modules

Do the checklist before submitting the PR:

• [:heavy_check_mark:] Have you read the guidelines mentioned in CONTRIBUTING.md?
• [:heavy_check_mark:] Have you squashed your commits?

Q: What version of Node.js you've used in the project? (e.g. Node v10.11.0) A:v11.10.1

Q: Mention the Issue Number! (e.g. Fixed #8) A:#112

• Give additional information regarding the PR below:

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[codecov-io]

Codecov Report

Merging #131 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #131    +/-   ##
======================================
  Coverage     100%   100%            
======================================
  Files          71     77     +6     
  Lines         934   1245   +311     
======================================
+ Hits          934   1245   +311

Impacted Files	Coverage Δ
src/validation/argument-length.js	100% <100%> (ø)
src/multiplication/index.js	100% <100%> (ø)
src/division/index.js	100% <100%> (ø)
src/absolute/index.js	100% <100%> (ø)
src/subtraction/index.js	100% <100%> (ø)
src/index.js	100% <100%> (ø)	:arrow_up:
src/addition/index.js	100% <100%> (ø)
... and 3 more

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