Spelling and grammar fixes.

[kratz00]

A couple of:

• spelling fixes
• grammar fixes
• formatting fixes

[schlimmchen]

Very nice, thank you!

There are two kinds of changes that I won't merge:

1. Changing iterations (numbered lists) to use incrementing indices in the source. This is not required as mkdocs/markdown knows that this is an iteration and that each new item must use a new index. Trying to use incrementing indices in the source is a problem, because one needs to update the whole list every time a new item is inserted in between existing items. That's why I just use "1." on every item in an iteration.
2. I don't want to format tables neatly in the source. Similarly to numbered lists, changing the table (like columns width because of one column enlarges) then prompts huge changesets, as the whole table needs to be reformatted. That is to be avoided. Also, I want to keep compatibility with the upstream version of the same table, so merging upstream changes isn't a PITA every time it is attempted.