Fix faust2mathdoc to convert all mathdoc SVG diagrams to PDF

[oneilltomhq]

Summary

• faust2mathdoc only converted process.svg in each mathdoc SVG directory, but --mathdoc can emit named <diagram>expr</diagram> SVGs that the generated .tex references as PDFs.
• Switch the main loop to use the existing convert_svgdirs2pdf helper (same approach as faust2mathviewer) so every generated .svg is converted before xelatex runs.
• Add tests/mathdoc/signalFlowPatternsMathdoc.dsp, a small repro with multiple <diagram> tags.

Problem

For DSP files with <diagram>parallel_tank</diagram> (and similar), faust --mathdoc writes SVGs like parallel-*.svg under *-mdoc/svg/svg-*/, and the TeX output references the corresponding PDFs. The script never created those PDFs, so xelatex failed with missing file errors:

! LaTeX Error: File `../svg/svg-01/parallel-0x...' not found.

Repro

faust2mathdoc tests/mathdoc/signalFlowPatternsMathdoc.dsp

Before this fix, only process.svg was converted (1 PDF for 39 generated SVGs); the named diagram PDFs were missing and xelatex aborted. After the fix, all 39 generated SVGs are converted and the PDF builds successfully (46 pages).

Test plan

• faust2mathdoc tests/mathdoc/signalFlowPatternsMathdoc.dsp completes and writes *-mdoc/pdf/*.pdf
• Verified 39 .svg files and 39 matching .pdf files under svg/
• Existing tests/mathdoc/rms.dsp still builds (no regression)

Notes

• Inkscape CLI flags left unchanged for compatibility.
• Missing supertabular (or similar LaTeX packages) on some systems is a separate dependency issue, not addressed here.

[sletz]

Is the PR ready now ?

[oneilltomhq]

@sletz I believe so - maybe the test file is a little sloppy in its substance - but the faust2mathdoc change allows multiple SVG diagrams, previously it was only allowing one