cameo: cleaned up and documented the tool compensation

- README, lang.l, lang.y: renamed the "tool" command to "offset"
- README: documented "offset"
- ops.h, ops.c (tool_comp_paths), cameo.c (main), lang.y: added
  parameter to tool_comp_paths to treat all paths as internal
- lang.l, lang.y: added option "inside" to the "offset" command
- lang.y: "offset" can now take multiple options in any order

cameo/README

@@ -110,4 +110,15 @@ Vertical adjustment:
 
 Tool compensation:
 
-  tool [dog]
+  offset [dog] [inside]
+
+"offset" offsets the toolpaths by the tool radius. By default, it offsets
+the outermost toolpath to the outside and all other toolpaths to the
+inside. This can be overridden with the #%outside directive in a gnuplot
+file or the "inside" option to "offset". "inside" has precedence over
+"#%outside".
+
+Concave corners on an outside path are normally cut such that the corner
+is round, leaving material at and near the corner point. The option "dog"
+changes this to cutting a "dogbone" hole such that material is also
+removed up to the corner point.