Add support to read from stdin

[abey79]

Description

Using - as file path is standard Unix to read from/to stdin/stdout instead of a file. The write command already supported -, but not the read command. This PR fixes this.

Checklist

• feature/fix implemented
• code formatting ok (black and isort)
• mypy vpype vpype_cli tests returns no error
• tests added/updated and pytest succeeds
• documentation added/updated
  • command docstring and option/argument help
  • README.md updated (Feature Overview)
  • CHANGELOG.md updated
  • RTD doc updated and building with no error (make clean && make html in docs/)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Merging #322 (078a42b) into master (ea7dadc) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #322      +/-   ##
==========================================
+ Coverage   92.06%   92.08%   +0.01%     
==========================================
  Files          50       50              
  Lines        3945     3954       +9     
  Branches      520      521       +1     
==========================================
+ Hits         3632     3641       +9     
  Misses        209      209              
  Partials      104      104              

Impacted Files	Coverage Δ
tests/test_files.py	100.00% <100.00%> (ø)
vpype/io.py	77.62% <100.00%> (ø)
vpype_cli/read.py	87.50% <100.00%> (+1.29%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ea7dadc...078a42b. Read the comment docs.