Handle tabs when parsing JSON

Fixes #539

src/main/resources/data/computercraft/lua/rom/apis/textutils.lua

@@ -432,7 +432,7 @@ do
 
     --- Skip any whitespace
     local function skip(str, pos)
-        local _, last = find(str, "^[ \n\r\v]+", pos)
+        local _, last = find(str, "^[ \n\r\t]+", pos)
         if last then return last + 1 else return pos end
     end
 
@@ -472,7 +472,7 @@ do
                     buf[n], n, pos = utf8.char(tonumber(num_str, 16)), n + 1, pos + 6
                 else
                     local unesc = escapes[c]
-                    if not unesc then error_at(pos + 1, "Unknown escape character %q.", unesc) end
+                    if not unesc then error_at(pos + 1, "Unknown escape character %q.", c) end
                     buf[n], n, pos = unesc, n + 1, pos + 2
                 end
             elseif c >= '\x20' then

src/test/resources/test-rom/data/json-parsing/y_tab_whitespace.json

@@ -0,0 +1 @@
+[	]