added new dictionary method to Hamiltonian class, and few other updates

[vishal-ph]

Description

• Added new method to Hamiltonian object that constructs a dictionary of terms (either PaulIOps or qubit indices) and coefficients of the Hamiltonian object
• added __hash__ method to PauliOp class, and fixed the __eq__ method.

Checklist

• [x] I have performed a self-review of my code.
• [x] I have commented my code and used numpy-style docstrings
• [x] I have made corresponding updates to the documentation.
• [x] My changes generate no new warnings
• [x] I have added/updated tests to make sure bugfix/feature works.
• [x] New and existing unit tests pass locally with my changes.

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Added a new unit-test in test_operators.py file to test the new method

[codecov[bot]]

Codecov Report

Merging #210 (a248b43) into dev (3278e64) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #210   +/-   ##
=======================================
  Coverage   97.72%   97.73%           
=======================================
  Files          37       37           
  Lines        6771     6789   +18     
=======================================
+ Hits         6617     6635   +18     
  Misses        154      154           

Impacted Files	Coverage Δ
tests/test_operators.py	100.00% <100.00%> (ø)
tests/test_qpu_devices.py	98.63% <100.00%> (ø)

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