Fixed some unclear definition docs in AppExtensionBase

[hvt]

Besides, fixed some obvious spelling mistakes in the same module.

[hvt]

@microsoft-github-policy-service agree company="IXON B.V."

[codecov[bot]]

Codecov Report

Merging #174 (669de1e) into dev (27bead7) will decrease coverage by 0.24%. The diff coverage is n/a.

:exclamation: Current head 669de1e differs from pull request most recent head b254938. Consider uploading reports for the commit b254938 to get more accurate results

@@            Coverage Diff             @@
##              dev     #174      +/-   ##
==========================================
- Coverage   90.51%   90.28%   -0.24%     
==========================================
  Files          53       53              
  Lines        3122     3046      -76     
  Branches      815      809       -6     
==========================================
- Hits         2826     2750      -76     
  Misses        219      219              
  Partials       77       77              

Flag	Coverage Δ
unittests	90.24% <ø> (-0.24%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
azure/functions/extension/app_extension_base.py	81.81% <ø> (ø)
azure/functions/extension/extension_meta.py	96.10% <ø> (ø)
...unctions/extension/function_extension_exception.py	100.00% <ø> (ø)

... and 2 files with indirect coverage changes