Output image baseline depth for INFO_MATH_IMAGES

* tta/perl/Texinfo/Convert/LaTeX.pm (convert_math_to_images):
Pass --depth option to dvipng and extract depth from command output.
* tta/perl/Texinfo/Convert/Plaintext.pm (_insert_image)
(_convert) [INFO_MATH_IMAGES],
* tta/perl/Texinfo/Convert/Info.pm (format_image):
output 'depth' value for @math.
5 files changed