[PSR-7] Ensure all incoming data for IncomingRequest are typed as arrays

- The docblocks indicated array, but the signatures had not been updated.
[PSR-7] Various edits

- Mainly grammar and punctuation changes, a few clarifications.
[PSR-7] Updates to the meta document

- Mainly clarifications in language.
Merge pull request #356 from weierophinney/hotfix/psr7-edits

[PSR-7] Edits for grammar, punctuation, clarity, consistency