ignore (some) empty field when converting csv

This fixes bug #733 and bug #734.
update baseline test for convert command
ignore extra fields when converting csv files

This fixes bug #736.
Merge pull request #89 from kljohann/bugs.convert

fix several ledger convert bugs
allow -f /dev/stdin in test runner
change handling of standard input

For `-f /dev/stdin`, the `pathname` of the parsing context will be empty
as for any other streamed input.

`instance_t::include_directive` did not work as expected for `-f /dev/stdin`
and relative file names. One would expect them to be relative to the current
directory rather than `/dev`.

This will lead to `While parsing file ""` messages. This could be
adjusted to read `While parsing standard input`, but maybe it's not
worth the special cases.

This commit also fixes bug 788: behaviour of source_context for '-f -'
Merge pull request #123 from kljohann/bug.788

change handling of standard input
Merge branch 'master' into next

Some commits were on the master branch but not yet on the next branch due to a
pull request to master after those two branches diverged. This merge
ensures that next ⊇ master.
only run doxygen once

To update the documentation run `ninja doxygen` or `make doxygen`.
update Doxyfile.in (using doxygen -u)
doxygen: enable search and folding
improve doxygen build logic

Doxygen will only be called when the 'doc' target is built
and one of its input files has changed.
do not auto-build documentation

Use 'ninja doc' or 'make doc' instead.