improved doc, fixed errors

@@ -49,12 +49,15 @@ special characters. Having `@@` in `s` inserts a single `@` in the
 result without using `args`, option `char='*'` allows to use `*`
 instead of `@` (or any other character). For instance:
 
-    tex("hello")         => hello
-    tex("\foo{@}", "$")  => \foo{\$}
-    tex("@@")            => @
-    tex("@@@+@@@", "x")  => @@@x@@@
+    tex("hello")                   => hello
+    tex(r"\foo{@}", "$")           => \foo{\$}
+    tex("@@")                      => @
+    tex("@@@+@@@", "x", char="+")  => @@@x@@@
+    
+So, string `s` is not escaped for LaTeX special characters, only the
+`args` are.
 
-Two more commands are available:
+Two more LaTeX commands are available:
 
  * `\pyc{pass}` inserts a pretty printed version of the Python snippet
    without evaluating it, environment `pycode` is similar but for a
@@ -84,5 +87,6 @@ Compile in three passes, like a bibTeX:
 Just run `latex -shell-escape jobname`. Pros: you use just one command
 and the results are inserted on the fly so everything is immediately
 consistent. Cons: it's slower (a server version of PyTeX is launched
-and communication takes some time, this may be improved in the
-future).
+and communication between `latex` and the server takes some time, this
+may be improved in the future if this is caused by PyTeX, but I
+suspect it is `\write18` mechanism that is slow).