Change canonicalization to normalization

[chisholm]

Back out references to canonicalization and change symbols, comments, etc to refer to normalization instead. If we're not really sure if we have a truly canonical form, better to play it safe.

[codecov-io]

Codecov Report

Merging #490 (ccaa8b6) into master (e513081) will not change coverage.
The diff coverage is 82.35%.

@@           Coverage Diff           @@
##           master     #490   +/-   ##
=======================================
  Coverage   89.33%   89.33%           
=======================================
  Files         147      147           
  Lines       16348    16348           
=======================================
  Hits        14605    14605           
  Misses       1743     1743           

Impacted Files	Coverage Δ
stix2/equivalence/pattern/compare/comparison.py	68.93% <ø> (ø)
stix2/equivalence/pattern/compare/observation.py	69.44% <ø> (ø)
stix2/equivalence/pattern/transform/comparison.py	73.01% <ø> (ø)
stix2/equivalence/pattern/transform/specials.py	78.35% <ø> (ø)
stix2/equivalence/pattern/transform/observation.py	75.93% <75.00%> (ø)
stix2/equivalence/pattern/__init__.py	74.28% <84.61%> (ø)

---

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 e513081...ccaa8b6. Read the comment docs.