Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Document that the *fsize() functions return a size of 1 for Elf
types that don't have a fixed size.
- The *fsize() functions should return a size of 1, for variable length
types.
- Redefine symbol ELF_T_LAST to match the current end of the list.

Obtained from: elftoolchain
MFC after: 1 month

Note that the *_fsize() functions are only defined for ELF types that
have a fixed size.

Obtained from: elftoolchain
MFC after: 1 month

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Document the return type for gelf_fsize(3).

Submitted by: kaiw

Fix minor formatting issues:

- make document title match filename;
- remove hard sentence breaks, whitespace at EOL, and double whitespace;
- sort SEE ALSO xrefs, adding missing section numbers;
- fix a misspelled macro name.

MFP4: Add an implementation of the ELF(3) and GELF(3) API set.

Bump __FreeBSD_version.

Reviewed by: jb