Sundry text changes, take two

Supersedes the self-closed PR
https://github.com/textpattern/pophelp/pull/6

Corrects 2x typos spotted by @Bloke, and includes some more uniformity
tidying - e.g., `folder` to `directory`.
Merge pull request #7 from petecooper/master

Sundry text changes, take two. Thanks Pete.