Fix typos

[guillemj]

This fixes lots of typos that end up in the generated output, possibly
in other projects, which would then be unable to fix these typos as they
will reappear when running asn1c again.

Warned-by: codespell

[coveralls]

Coverage remained the same at 70.906% when pulling 7ee8e43 on guillemj:pu/typos into fdb68ce on vlm:master.

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