Send Formatted Text r0.6.0

[TheDiscordian]

Adds:

// SendFormattedText sends an m.room.message event into the given room with a msgtype of m.text, supports a subset of HTML for formatting.
// See https://matrix.org/docs/spec/client_server/r0.6.0#m-text
func (cli *Client) SendFormattedText(roomID, text, formattedText string) (*RespSendEvent, error) {

[TheDiscordian]

This might conflict with #58's intent.