[WIP] Release 0.2.1 cherry-picks

[ritzvik]

Fixes #<Put_Issue_Number_Here>

[pep8speaks]

Hello @ritzvik! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file src/einsteinpy/symbolic/constants.py:

Line 6:55: W291 trailing whitespace
Line 11:55: W291 trailing whitespace
Line 14:43: W291 trailing whitespace
Line 15:47: W291 trailing whitespace
Line 46:30: W291 trailing whitespace
Line 48:1: W293 blank line contains whitespace

• In the file src/einsteinpy/symbolic/einstein.py:

Line 24:121: E501 line too long (134 > 120 characters)

• In the file src/einsteinpy/symbolic/tensor.py:

Line 188:55: W291 trailing whitespace
Line 189:62: W291 trailing whitespace
Line 206:1: W293 blank line contains whitespace
Line 207:1: W293 blank line contains whitespace
Line 222:1: W293 blank line contains whitespace
Line 228:77: W291 trailing whitespace
Line 231:121: E501 line too long (134 > 120 characters)
Line 235:121: E501 line too long (122 > 120 characters)
Line 235:123: W291 trailing whitespace
Line 238:69: W291 trailing whitespace
Line 306:1: W293 blank line contains whitespace

• In the file src/einsteinpy/symbolic/vector.py:

Line 22:121: E501 line too long (133 > 120 characters)
Line 54:55: W291 trailing whitespace
Line 55:110: W291 trailing whitespace

• In the file src/einsteinpy/symbolic/weyl.py:

Line 26:121: E501 line too long (136 > 120 characters)
Line 89:29: W503 line break before binary operator
Line 90:29: W503 line break before binary operator
Line 91:29: W503 line break before binary operator
Line 93:25: W503 line break before binary operator
Line 95:21: W503 line break before binary operator
Line 97:25: W503 line break before binary operator
Line 98:25: W503 line break before binary operator

• In the file src/einsteinpy/tests/test_symbolic/test_tensor.py:

Line 72:12: E713 test for membership should be 'not in'

[ritzvik]

@shreyasbapat Let's gear up for 0.2.1 .
I was not sure whether to include commits of #318 , I don't think changing package dependencies should happen between patch releases.

Anyways, waiting for #316 , #286

[codecov]

Codecov Report

Merging #323 into 0.2.x will increase coverage by 0.28%.
The diff coverage is 96.03%.

@@            Coverage Diff            @@
##           0.2.x     #323      +/-   ##
=========================================
+ Coverage   93.7%   93.98%   +0.28%     
=========================================
  Files         37       40       +3     
  Lines       1351     1514     +163     
=========================================
+ Hits        1266     1423     +157     
- Misses        85       91       +6

Impacted Files	Coverage Δ
src/einsteinpy/bodies.py	100% <ø> (ø)	⬆️
src/einsteinpy/symbolic/stress_energy_momentum.py	100% <100%> (ø)	⬆️
src/einsteinpy/symbolic/christoffel.py	97.05% <100%> (-0.62%)	⬇️
src/einsteinpy/symbolic/riemann.py	95% <100%> (+1.12%)	⬆️
src/einsteinpy/symbolic/__init__.py	100% <100%> (ø)	⬆️
src/einsteinpy/symbolic/metric.py	100% <100%> (ø)	⬆️
src/einsteinpy/symbolic/constants.py	100% <100%> (ø)
src/einsteinpy/symbolic/einstein.py	100% <100%> (ø)	⬆️
src/einsteinpy/symbolic/tensor.py	95.69% <90%> (-2.72%)	⬇️
src/einsteinpy/symbolic/vector.py	94.11% <94.11%> (ø)
... and 6 more

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[shreyasbapat]

We can make this release after the SOCIS period is over.

[shreyasbapat]

This PR needs to hold as of now! But I will make sure that all the Symbolic related cherry picks are included. One of my PR will supersede it once #327 is merged!

[shreyasbapat]

And. DON'T DELETE YOUR BRANCH!