ansi: show ANSI art in a UTF-8 terminal, or as plain or shaded text

Draws an .ans file into a grid the way an ANSI-BBS terminal would (cursor
moves, the wrap at the SAUCE width, iCE colours) and writes it out as UTF-8:
in colour, --plain, or --mono with coloured areas shaded by brightness. info
prints the SAUCE record. One C99 file with no dependencies.

README.md

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+# ansi
+
+Show ANSI art in a modern terminal, or turn it into plain text.
+
+An `.ans` file is CP437 text with ANSI colour and cursor codes, laid out for an
+80-column BBS terminal that wraps it. Converting it with `iconv` gets the
+characters right but not the layout: a lot of art has no line breaks at all, and
+much of it moves the cursor around. `ansi` draws the file into a grid the way a
+BBS terminal would, then writes the grid out as UTF-8 lines.
+
+```console
+$ ansi piece.ans | less -R          # in colour
+$ ansi --mono piece.ans > piece.txt # no colour, coloured areas as shading
+$ ansi --plain piece.ans            # the characters only
+$ ansi info piece.ans               # title, artist, group, date and size
+$ curl -s https://16colo.rs/pack/dd26/raw/dd-cola.ans | ansi
+```
+
+`--mono` is for places that show no colour, like newsgroups and mail. Each
+coloured area is redrawn by how bright its colour looks, so art built from
+coloured spaces keeps its shape instead of going blank.
+
+It follows the SAUCE record for the width, shows blinking backgrounds bright
+(iCE colour), and reads standard input when given no file or `-`.
+
+## Install
+
+One C99 file, no dependencies.
+
+```console
+$ make
+$ make install               # into ~/bin and ~/share/man/man1
+$ make install PREFIX=/usr/local
+```
+
+## Licence
+
+GPL-2.0. See `LICENSE`.