Bot login and proxy support

Scheme layer used: 62

This release features:

• Bot login, thanks to @JuanPotato for hinting me about how to do it.
• Proxy support, thanks to @exzhawk for implementing it.
• Logging support, used by passing --telethon-log=DEBUG (or INFO) as a command line argument.

With the following bug fixes:

• Connection fixes, such as avoiding connection until .connect() is explicitly invoked.
• Uploading big files now works correctly.
• Fix uploading big files.
• Some fixes on the updates thread, such as correctly sleeping when required.