Add requirement for python-magic, and add wrappers to Mastodon.py

.gitignore

@@ -91,4 +91,6 @@ ENV/
 # Secret files (for credentials used in testing)
 *.secret
 pytooter_clientcred.txt
-pytooter_usercred.txt
+pytooter_usercred.txtPipfile
+Pipfile.lock
+Pipfile

mastodon/Mastodon.py

@@ -31,6 +31,11 @@ try:
 except ImportError:
     from urlparse import urlparse
 
+try:
+    import magic
+except ImportError:
+    magic = None
+
 ###
 # Version check functions, including decorator and parser
 ###
@@ -2529,3 +2534,11 @@ class MastodonRatelimitError(MastodonError):
 class MastodonMalformedEventError(MastodonError):
     """Raised when the server-sent event stream is malformed"""
     pass
+
+def guess_type(media_file):
+    mime_type = None
+    if magic:
+        mime_type = magic.from_file(media_file, mime=True)
+    else:
+        mime_type = mimetypes.guess_type(media_file)[0]
+    return mime_type

setup.py

@@ -14,6 +14,7 @@ setup(name='Mastodon.py',
           'python-dateutil', 
           'six', 
           'pytz',
+          'python-magic',
           'decorator>=4.0.0', 
           'http_ece>=1.0.5',
           'cryptography>=1.6.0'