Add more licensing info

[ttmc]

• Added a new file LICENSE-docs to specify the license on all the docs.
• Edited README.md: changed the Licensing section to just point to the files LICENSE and LICENSE-docs.
• Added comments to all source files, to give the licensing information (using the add-spdx script).
• Removed the "coding: utf-8" line from conf.py because that line is not needed in Python 3 files.

[codecov-io]

Codecov Report

Merging #235 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #235   +/-   ##
=======================================
  Coverage   94.96%   94.96%           
=======================================
  Files          11       11           
  Lines         258      258           
=======================================
  Hits          245      245           
  Misses         13       13

Impacted Files	Coverage Δ
src/stringify_as_query_param.js	90% <ø> (ø)	:arrow_up:
src/utils/ccJsonLoad.js	100% <ø> (ø)	:arrow_up:
src/utils/ccJsonify.js	80.76% <ø> (ø)	:arrow_up:
src/connection.js	100% <ø> (ø)	:arrow_up:
src/baseRequest.js	86.2% <ø> (ø)	:arrow_up:
src/sha256Hash.js	100% <ø> (ø)	:arrow_up:
src/Ed25519Keypair.js	100% <ø> (ø)	:arrow_up:
src/request.js	92.85% <ø> (ø)	:arrow_up:
src/format_text.js	100% <ø> (ø)	:arrow_up:
src/sanitize.js	100% <ø> (ø)	:arrow_up:
... and 1 more

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