Merge iostreams changes.
Merge iostreams. Release notes + more support for sun.
Merge some fixes from trunk:

 - Missing newline in an iostreams header.
 - Link fixes for iostream documentation.
 - Ignore a doxygen tag in boostbook.
Merge iostreams.

 - Fix write_device_impl<ostream_tag>. Fixes #3839
 - Fix error checks after calling SetFilePointer. Fixes #3953
 - Gzip filter shouldn't require its source to be peekable. Fixes #3723.
 - In `position_to_offset`, only cast to `stream_offset` after calculating
   `_Myoff`. Fixes #3969.
 - ptrdiff_t is in std. Fixes #2505.
Small iostreams merge.

 - Minor test fix for some compilers.
 - Inspect fix.
Try to avoid a warning.
Merge iostreams link fixes.
Merge some link fixes and release notes.
Merge iostreams. Fixes #4135 and some small tweaks for clang.
Small documentation fixes.
Merge iostreams from the trunk.
Merge documentation fixes.

* Use `doc/src/*.css` instead of `doc/html/*.css`.
* Remove wiki and people directories.
* Some documentation fixes.
* Left out `minimal.css` changes and boostbook changes because of clashes.
Merge iostreams.

* New constructors/`open` for file descriptors.
  Fixes #3517.
* Use `unique_path` instead of tmpnam. Refs #2325.
Revert iostreams merge.
Partially merge iostreams.

* New constructors/`open` for file descriptors.
  Fixes #3517.
* Leaving out changes which depend on filesystem v3.
Use unique_path instead of tmpnam. Refs #2325.
Merge iostreams, hash.

Including disallowing implicit casts to `hash_value`.
Merge quickbook, iostreams.
Merge some link fixes.

[64006] and [64059].
Merge iostreams html fix.