Speed comparison

```
time md2html README.md > /dev/null

real    0m1.260s
user    0m1.212s
sys 0m0.043s
```

```
time rst2html.py README.rst > /dev/null

real    0m0.173s
user    0m0.148s
sys 0m0.022s
```

```
time markdown_py README.md > /dev/null

real    0m0.056s
user    0m0.042s
sys 0m0.012s
```

Looks like that parsley seems at fault but still it is a good idea to keep that in mind.
