Added Serial BFS

[czgdp1807]

References to other Issues or PRs or Relevant literature

#82

Brief description of what is fixed or changed

Other comments

[codecov]

Codecov Report

Merging #126 into master will decrease coverage by 0.063%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##           master      #126       +/-   ##
============================================
- Coverage   97.94%   97.876%   -0.064%     
============================================
  Files          20        21        +1     
  Lines        1311      1460      +149     
============================================
+ Hits         1284      1429      +145     
- Misses         27        31        +4

Impacted Files	Coverage Δ
pydatastructs/__init__.py	100% <100%> (ø)	⬆️
pydatastructs/graphs/algorithms.py	100% <100%> (ø)
pydatastructs/utils/misc_util.py	97.368% <100%> (ø)	⬆️
pydatastructs/graphs/graph.py	100% <100%> (ø)	⬆️
pydatastructs/graphs/__init__.py	100% <100%> (ø)	⬆️
pydatastructs/trees/binary_trees.py	96.651% <0%> (-0.514%)	⬇️
pydatastructs/linear_data_structures/__init__.py	100% <0%> (ø)	⬆️
...datastructs/linear_data_structures/linked_lists.py	100% <0%> (ø)	⬆️