- Add mime.types file to contain a good database of type -> ext mappings
from svn.apache.org/repos/asf/httpd/httpd/trunk/docs/conf/mime.types
- Load mime.type at BaseClient creation and add two convenience methods
for guessing mime types from filenames and extensions from mime types,
guess_mime_type and guess_extension
- Make all send_* method as well as download_media use the new mime type
database via guess_mime_type and guess_extension methods
With the Bot API 4.0 update (https://core.telegram.org/bots/api#july-26-2018), sendAudio allows bots to pass a thumbnail - making it possible for pyrogram to include a 'thumb' parameter in its convenience method 'send_audio'