Added DoublyLinkedList

[czgdp1807]

References to other Issues or PRs or Relevant literature

Closes #51
#49

Brief description of what is fixed or changed

Other comments

[codecov]

Codecov Report

Merging #55 into master will increase coverage by 0.172%.
The diff coverage is 99.371%.

@@              Coverage Diff              @@
##            master       #55       +/-   ##
=============================================
+ Coverage   98.005%   98.177%   +0.172%     
=============================================
  Files           17        19        +2     
  Lines         1103      1262      +159     
=============================================
+ Hits          1081      1239      +158     
- Misses          22        23        +1

Impacted Files	Coverage Δ
pydatastructs/utils/__init__.py	100% <ø> (ø)	⬆️
...datastructs/linear_data_structures/linked_lists.py	100% <100%> (ø)
pydatastructs/linear_data_structures/__init__.py	100% <100%> (ø)	⬆️
pydatastructs/utils/raises_util.py	100% <100%> (ø)	⬆️
.../linear_data_structures/tests/test_linked_lists.py	100% <100%> (ø)
pydatastructs/utils/misc_util.py	95.833% <90%> (-4.167%)	⬇️