MIGRATE-0.10.md

There are many API changes from 0.9 to 0.10 and most probably you'll need to migrate your code. This is the summary of breaking changes:

• the crate uses edition = "2018" thus requiring rust-1.31
• Connection consumes Context on creation and releases it on connect_*(), allows to avoid using Arc and provides more safety
• type signatures for Connection, Context have an additional lifetime arg
• Connection::context() is removed, context is now passed as the first argument to a callback
• Connection and Logger own the callbacks supplied to them, passing closure references is still possible, all callbacks must be Send
• Connection::*handler_add() return special handles used to remove callbacks later
• Connection::*handler_delete() take special handles returned from Connection::*handler_add() and not callback references
• Context implements memory allocation through Rust allocator
• Context::set_timeout() takes &mut self instead of &self
• the crate uses failure instead of error-chain
• StreamError no longer implements std::error::Error
• Stanza::context() is no longer accessible publicly
• Stanza::get_first_child_mut() takes &mut self instead of &self