fitstopnm, pamcut, pamdeinterlace, pamdice, pammixinterlace, pamtofits, pamundice, pnmtofits: add pages (#12296)

* fitstopnm, pamcut, pamdeinterlace, pamdice, pammixinterlace, pamtofits, pamundice, pnmtofits: add pages

* Apply suggestions from code review

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

* Update pages/common/pamdice.md

* Update pages/common/fitstopnm.md

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

* Update pages/common/fitstopnm.md

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

* Update pages/common/pamundice.md

---------

Co-authored-by: Vitor Henrique <87824454+vitorhcl@users.noreply.github.com>

pages/common/pammixinterlace.md

@@ -0,0 +1,17 @@
+# pammixinterlace
+
+> Merge each row in an image with its two neighbours.
+> See also: `pamdeinterlace`.
+> More information: <https://netpbm.sourceforge.net/doc/pammixinterlace.html>.
+
+- Merge each row in an image with its two neighbours:
+
+`pammixinterlace {{path/to/image.ppm}} > {{path/to/output.ppm}}`
+
+- Use the specified filtering mechanism:
+
+`pammixinterlace -filter {{linear|fir|ffmpeg}} {{path/to/image.ppm}} > {{path/to/output.ppm}}`
+
+- Turn on adaptive filtering mode, i.e., only modify pixels that are obviously part of a comb pattern:
+
+`pammixinterlace -adaptive {{path/to/image.ppm}} > {{path/to/output.ppm}}`