Feature/matchers

Hi 

Thank you for `vcrpy` !

This pull request contains some test for matchers and also additional 'semantic_url' matcher.
The idea behind it is very simple just compare urls without strict comparison of params ordering in query string. 
The reason is when you do a request with for example `requests` like 
```
payload = {'key1': 'value1', 'key2': 'value2'}
r = requests.get("http://httpbin.org/get", params=payload)
```
Then ordering of the params in query string can't be preserved and it leads to non matching by existing 'url' matcher.
The proposed solution is not good because I think the  better solution could be like this:
```
def url(r1,r2):
      return host(r1,r2) and path(r1,r2) and query_string(r1, r2) ...
```
But I think it is better to start with small changes first (because it is my first pull request ).

Regards,
Max