Metadata 2.1 updates

[di]

Fixes #231:

• Set Metadata-Version to 2.1
• Don't create a DESCRIPTION.rst

(ping @agronholm)

[codecov]

Codecov Report

Merging #232 into master will decrease coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #232      +/-   ##
==========================================
- Coverage   70.13%   70.04%   -0.09%     
==========================================
  Files          18       18              
  Lines        1818     1813       -5     
==========================================
- Hits         1275     1270       -5     
  Misses        543      543

Impacted Files	Coverage Δ
wheel/metadata.py	91.38% <100%> (ø)	⬆️
wheel/bdist_wheel.py	55.97% <100%> (-0.81%)	⬇️

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[9999years]

What’s left before this can get merged? Eager to help.

[di]

@agronholm said on #pypa-dev:

it's only waiting for me to get some free time, possibly later today

[agronholm]

Thanks!