pamfunc, ppmchange, ppmcie, ppmcolormask, ppmdim, ppmdist, ppmfade, ppmforge: add pages (#11449)

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/common/ppmchange.md

@@ -0,0 +1,16 @@
+# ppmchange
+
+> Change all pixels of one color in a PPM image to another color.
+> More information: <https://netpbm.sourceforge.net/doc/ppmchange.html>.
+
+- Exchange the first color in each `oldcolor` - `newcolor` pair with the second color:
+
+`ppmchange {{oldcolor1 newcolor1 oldcolor2 newcolor2 ...}} {{path/to/input.ppm}} > {{path/to/output.ppm}}`
+
+- Specify how similar colors must be in order to be considered the same:
+
+`ppmchange -closeness {{percentage}} {{oldcolor1 newcolor1 oldcolor2 newcolor2 ...}} {{path/to/input.ppm}} > {{path/to/output.ppm}}`
+
+- Replace all pixels not specified in the arguments by a color:
+
+`ppmchange -remainder {{color}} {{oldcolor1 newcolor1 oldcolor2 newcolor2 ...}} {{path/to/input.ppm}} > {{path/to/output.ppm}}`