package .bin/ scripts as proper nix packages, delete .bin/

Packaged 14 scripts from .bin/ into packages/ with proper dependency
declarations (writers.writeDashBin/writeBashBin/writePython3Bin):
- 256color → two56color (terminal color chart)
- avesta.sed → avesta (Avestan transliteration)
- bvg.sh → bvg (Berlin transit disruptions)
- unicode → charinfo (Unicode character info)
- chunk-pdf → chunk-pdf (split PDFs by page count)
- csv2json → csv2json (CSV to JSON converter)
- fix-sd.sh → fix-sd (exFAT SD card recovery, improved output handling)
- json2csv → json2csv (JSON to CSV converter)
- mp3player-write → mp3player-write (audio conversion for MP3 players)
- mushakkil.sh → mushakkil (Arabic diacritization)
- nix-haddock-index → nix-haddock-index (GHC Haddock index generator)
- pdf-ocr.sh → pdf-ocr (OCR PDFs via tesseract)
- prospekte.sh → prospekte (German supermarket flyer browser)
- readme → readme (GitHub README as man page)

All added to overlay and packages output. .bin/ directory removed.

packages/readme.nix

@@ -0,0 +1,12 @@
+# Render a GitHub repo's README.md as a man page
+{
+  writers,
+  curl,
+  pandoc,
+  man,
+}:
+writers.writeDashBin "readme" ''
+  ${curl}/bin/curl -sSL "https://raw.githubusercontent.com/$*/master/README.md" \
+    | ${pandoc}/bin/pandoc -f gfm -t man -s \
+    | ${man}/bin/man -l -
+''