method __str__ from UserAgent now using methods (#94)

Is better to calculate and provide a method to calculate the string values for `device`, `os` and `browser`  instead of doing it  directly on `__str__` method. 

This way the users may use those methods to get each data directly. Instead of having to make a `user_agent.__str__().split('/')` to get each value

Author: rodrigondec

user_agents/parsers.py

@@ -140,10 +140,11 @@ def __init__(self, user_agent_string):
         self.device = parse_device(**ua_dict['device'])
 
     def __str__(self):
-        device = self.is_pc and "PC" or self.device.family
-        os = ("%s %s" % (self.os.family, self.os.version_string)).strip()
-        browser = ("%s %s" % (self.browser.family, self.browser.version_string)).strip()
-        return " / ".join([device, os, browser])
+        return "{device} / {os} / {browser}".format(
+            device=self.get_device(),
+            os=self.get_os(),
+            browser=self.get_browser()
+        )
 
     def __unicode__(self):
         return unicode(str(self))
@@ -167,6 +168,15 @@ def _is_blackberry_touch_capable_device(self):
             return True
         return False
 
+    def get_device(self):
+        return self.is_pc and "PC" or self.device.family
+
+    def get_os(self):
+        return ("%s %s" % (self.os.family, self.os.version_string)).strip()
+
+    def get_browser(self):
+        return ("%s %s" % (self.browser.family, self.browser.version_string)).strip()
+
     @property
     def is_tablet(self):
         if self.device.family in TABLET_DEVICE_FAMILIES:
@@ -255,5 +265,6 @@ def is_email_client(self):
             return True
         return False
 
+
 def parse(user_agent_string):
     return UserAgent(user_agent_string)