Clear gets an option to reset the palette (#582)

Fixes #555.

src/main/resources/data/computercraft/lua/rom/help/clear.txt

@@ -1 +1,6 @@
-clear clears the screen.
+clear clears the screen and/or resets the palette.
+ex:
+"clear" clears the screen, but keeps the palette.
+"clear screen" does the same as "clear"
+"clear palette" resets the palette, but doesn't clear the screen
+"clear all" clears the screen and resets the palette

src/main/resources/data/computercraft/lua/rom/programs/clear.lua

@@ -1,2 +1,33 @@
-term.clear()
-term.setCursorPos(1, 1)
+local tArgs = { ... }
+
+local function printUsage()
+    local programName = arg[0] or fs.getName(shell.getRunningProgram())
+    print("Usages:")
+    print(programName)
+    print(programName .. " screen")
+    print(programName .. " palette")
+    print(programName .. " all")
+end
+
+local function clear()
+    term.clear()
+    term.setCursorPos(1, 1)
+end
+
+local function resetPalette()
+    for i =  0, 15 do
+        term.setPaletteColour(math.pow(2, i), term.nativePaletteColour(math.pow(2, i)))
+    end
+end
+
+local sCommand = tArgs[1] or "screen"
+if sCommand == "screen" then
+    clear()
+elseif sCommand == "palette" then
+    resetPalette()
+elseif sCommand == "all" then
+    clear()
+    resetPalette()
+else
+    printUsage()
+end

src/main/resources/data/computercraft/lua/rom/startup.lua

@@ -49,6 +49,7 @@ end
 
 shell.setCompletionFunction("rom/programs/alias.lua", completion.build(nil, completion.program))
 shell.setCompletionFunction("rom/programs/cd.lua", completion.build(completion.dir))
+shell.setCompletionFunction("rom/programs/clear.lua", completion.build({ completion.choice, { "screen", "palette", "all" } }))
 shell.setCompletionFunction("rom/programs/copy.lua", completion.build(
     { completion.dirOrFile, true },
     completion.dirOrFile