improved seq() documentation wording

Two changes were made here:

- `latter` was changed to `former` (that caused a good deal of headache the other day)
- added some clarification as to what exactly differs from the `compose()` function

Since it's not entirely clear that `compose()` doesn't work left to right, `seq()` should better indicate that it does.
Improve documentation for async.seq

- seq requires the last argument to be a function
- seq short-circuits on errors which means using handleError is redundant
Fix incorrect sample code
Further clarification, link compose
Merge branch 'Qix--patch-1'