Style specification for building *.ind from *.idx. This is needed to avoid

wrapping of long lines, which tools/indfix.py doesn't understand, and needs
to to handle collapsing of entries which can share a common emtry and just
be short entries themselves.  We get the added benefit of nicer formatting.

Doc/texinputs/myindex.ist

+line_max 100
+headings_flag 1
+heading_prefix "  \\bigletter "
+
+preamble "\\begin{theindex}
+\\def\\bigletter#1{{\\Large#1}\\vspace{1mm}}
+
+"
+
+symhead_positive "{Symbols}"
+numhead_positive "{Numbers}"