Add the inplace version of the einsum function

[GiggleLiu]

Related issues:

• inplace interface #75
• [Feature request] Inplace version einsum function #148

[codecov-commenter]

Codecov Report

Attention: 47 lines in your changes are missing coverage. Please review.

Comparison is base (5bc5cc8) 88.82% compared to head (ef84f09) 89.32%.

Files	Patch %	Lines
ext/CUDAExt.jl	0.00%	40 Missing ⚠️
src/matchrule.jl	95.00%	5 Missing ⚠️
src/einsum.jl	99.19%	1 Missing ⚠️
src/utils.jl	97.61%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #159      +/-   ##
==========================================
+ Coverage   88.82%   89.32%   +0.49%     
==========================================
  Files          12       14       +2     
  Lines         975     1030      +55     
==========================================
+ Hits          866      920      +54     
- Misses        109      110       +1     

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