Branch to work on filename handling without disturbing trunk.
Use generic string for `__FILENAME__`.

Will hopefully a bit more consistent across platforms. Obviously proper
conversion to UTF-8 would be better.
Change the way the filename is stored.

No longer stored in the iterator which means there's less messing around
with pointers and strings. Always stored as a fs::path which will help
with support for unicode. Also passed to outwarn and outerr as fs::path
so they can handle writing unicode filenames to the output.
Use fs::path in more places.
Use filesystem alias more consistently.
Replace input_path with manual path conversion.
Use a function to convert paths to and from utf-8.

This will eventually try to cope with unicode characters. Not sure if
it'll ever be truely cross platform.
Windows support for unicode filenames.
Fix class/struct warning.
Move error and warning functions into input_path.

I'll rename it after merging with trunk. I'm just collecting all the
input and output functions together.
Turn debug symbols off when testing quickbook.

Fixes an odd error with the Boost Build Visual C++ tool.
Support for wide output streams on windows.
Fix default output filename.
Add ids to bridgeheads.

Prevents docbook from making up ever changing ids. It would be nice to
use the heading's anchor. But that causes docbook to complain that it
can't generate a title for the link.
Nicer link break warnings.
Check for portable paths in more places.
Fix rooted path handling on windows.

Was using `!path.is_complete()` to check if a path is relative - this
doesn't work on windows since paths like `\a\b` and `c:foo` aren't
complete or absolute. So now use
`!path.has_root_directory && !path.has_root_name()` instead.
Partial fix for portable path detection.

`portable_posix_name` is for checking names not paths. So instead just
warn if the path contains a `\` which is close enough. Should really be
using URLs. Maybe converting `\` to `/` (with a warning) for backwards
compatability.
Get the quickbook test tool working from other directories.
Count lines and columns from 1 in the quickbook iterator.