version bump
Added Mac OS X to compatible plattforms
Added installation notes for OS X
Fixed Regex for URLS

The old regex wouldn't match several characters at once, just the first one, so I added a + inside the parentheses.

I also got rid of the $, as it seemed unnecessary. Things like a trailing slash, or other miscellaneous params added to the URL could ruin that. In order to make sure we only got the id, I also added # and ?, which are two other common url patterns that we wouldn't want to capture anything after.

Other alternatives: 

If you just want to get rid of a possible trailing slash: 

```
mo = re.search("^https?://www.infoq.com/presentations/([^/]+)/?$", name) 
```

If you want to assume that the id will always be alphanumeric + hyphens,

```
mo = re.search("^https?://www.infoq.com/presentations/([0-9A-za-z-]+)", name) 
```
Add test for "presentation download URL", issue #19
Fix #16: Handle already existing file

Cleanly exit if the output file already exists.
Add --overwrite/-y option to overwrite the existing file.

Thanks to Lee Hanxue <hanxue.developer@gmail.com> for
having reported the issue and provided a patch.
Merge branch 'develop'

Conflicts:
	setup.py