The way tesstrain.sh handled font names was really weird, using '+'
signs as a delimiter. However quoting arguments is a much more
straightforward, standard and sensible way to do things.
So whereas previously one would have used this:
--fontlist Times New Roman + Arial Black
Now they should be specified like this:
--fontlist "Times New Roman" "Arial Black"
mktemp is a better idea for security, as well as enabling users to
specify a different directory using the TMPDIR environment variable,
which is useful if /tmp is a small tmpfs.
Also fix a bug where the first few log messages were failing as the
workspace directory wasn't been created early enough.
This flag can be used to specify multiple different exposure levels
for a training. There was some code already in tesstrain_utils.sh
to deal with multiple exposure levels, so it looks like this
functionality was always intended.
The default usage does not change, with exposure level 0 being the
only one used if --exposures is not used.
The --bin_dir option to tesstrain.sh is not useful, as $PATH does the
same job much better, so switch to relying on that instead.
This also makes the code a bit more readable, as it removes the need
to refer to binaries as COMMAND_NAME_EXE rather than just command_name.
