updated user send syntax to match room send, add configurable message-format

[flyinbutrs]

Apologies, on #168, I accidentally caused the syntaxes of the room send and direct send to diverge. This fixes that divergence.

before:

hc.user(user).send(message, 'text', true)

after:

hc.user(user).send(message, message_format: 'text', notify: true)