Pack arguments to BBD callbacks
Revise ambiguous wording

In the passage
"The difference quotient operation is controlled by [?dqrely],
 the relative increment in components of [y], and {!bandwidths}"
the commas look like serial commas rather than parenthetical commas.
Fix intro.doc

- Correct wording/punctuation and some factual errors
- Add note on how to select features with ocamlfind
- Note on testing parallel features from custom toplevel
- Show how to type-annotate an entire function rather than its arguments
Fix META.in: package name sundials -> sundialsml
Expand on comment in nvector_array.ml

This module is meant to be be seen by users as an example of how to
write custom, so it should be relatively easy to understand.
Minor bug fix in configure
Detect nvec_parallel in configure
Re-generate META when re-configured
fixup! 3cbe583 Fix intro.doc
Check sizeof (realtype) in configure
Streamline order of tests in configure

1. Detect and classify C compiler
2. Detect Sundials/C and check ABI compatibility
3. Detect OCaml and check ABI compatibility
4. Check availability of optional features