Added str methods for ODA and DODA

[HarsheetKakar]

References to other Issues or PRs or Relevant literature

Brief description of what is fixed or changed

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[codecov]

Codecov Report

Merging #208 into master will increase coverage by 0.012%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master      #208       +/-   ##
=============================================
+ Coverage   96.876%   96.889%   +0.012%     
=============================================
  Files           24        24               
  Lines         1921      1929        +8     
=============================================
+ Hits          1861      1869        +8     
  Misses          60        60               

Impacted Files	Coverage Δ
pydatastructs/linear_data_structures/arrays.py	100.000% <100.000%> (ø)

[HarsheetKakar]

Is this ready to move?