Fix misspellings in docs, comments, and strings.

I fixed various misspellings.
We should be consistent in AE vs. BE spelling. Parameteri<b>s</b>ed is British, parameteri<b>z</b>ed is American. I'm not sure what is standard in Elixir, but since we talk about behavio<b>u</b>rs then maybe BE? (In that case, line 21 should be `Parameterised`.)