Automatically download standalone language server package

[tetron]

1. Scripted build of standalone binary packages of benten-ls using PyInstaller. (make_binary_package.py)
2. Modify benten vscode-client to automatically download and untar the appropriate binary package for the platform & use it
3. Now expects that vscode client and benten-ls versions are synchronized (this means if you update the vscode plugin it'll automatically get the language server package corresponding to the update).

To do:

• See about building binary package on MacOS
• Decide where to host the binary packages
• Ideally, set up a multi-platform CI system like AppVeyor to build PyInstaller packages for each platform automatically (PyInstaller does not cross compile). However we can do an initial release with manually-built packages.

[codecov-io]

Codecov Report

Merging #103 (9583ba5) into master (3630ec9) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage   70.33%   70.30%   -0.03%     
==========================================
  Files          40       40              
  Lines        2043     2041       -2     
==========================================
- Hits         1437     1435       -2     
  Misses        606      606              

Impacted Files	Coverage Δ
benten/configuration.py	87.23% <100.00%> (-0.27%)	⬇️
benten/cwl/specification.py	97.56% <100.00%> (-0.03%)	⬇️

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[tetron]

This is superceded by the kg/dist-install branch