Added a Travis CI script.

Also added the requirements.txt file, after
mkdocs & nose installation.

It must be more accurate than the file extension.

Allow empty title for code snippets. It may
be useful for short code fragments.

Always use UTF-8 as it is commonly used
for platform-independent source files.

The fix in 2979ea4
was incomplete: see the added tests.

Use the last line indent so that the result can be
un-indented by the caller. It prevents results like this:

```
    /* block 1 */
...
    /* block 2 */
```

turning them into

```
    /* block 1 */
    ...
    /* block 2 */
```

which will be dedented by the caller.