texstring is a pair of a docstring and a corresponding TexRow. The row count in
the TexRow has to match the number of lines in the docstring.
otexstringstream is an output string stream that can be used to create
texstrings (i.e. it's an odocstringstream that records the TexRow information
and let us extract a texstring from it).
texstrings can be passed around and output to otexstream and otexrowstream,
which produces an accurate TexRow information by concatenating TexRows.
Please use the new function otexstream.append(str, texrow) to append an
odocstringstream with texrow information to the output when outputing to a
string buffer (e.g. case of subcaptions).
otexstream used to count lines to build a TexRow, and some other things. The new
class otexrowstream has the line counting feature of the previous otexstream
without other stuff. otexstream is now a subclass of otexrowstream that has the
same features as before.
This is preliminary work for extending the cursor<->row tracking to math.
This resolves a dependency of src/support/docstream.cpp on src/TexRow.cpp,
which is the wrong way round. This fixes the linking
src/tests/check_ExternalTransforms with MSVC where the linker is not clever
enough to detect that the whole otexstream class is unused.
