# Prepares the connection and sets defaults for any future requests.
#
# @param [String] url The destination URL
# @param persistent [Boolean]
# @param [Hash] params
# @option params [String] :body Default text to be sent over a socket. Only used if :body absent in Connection#request params
# @option params [Hash<Symbol, String>] :headers The default headers to supply in a request. Only used if params[:headers] is not supplied to Connection#request
# @option params [String] :host The destination host's reachable DNS name or IP, in the form of a String
# @option params [String] :path Default path; appears after 'scheme://host:port/'. Only used if params[:path] is not supplied to Connection#request
# @option params [Fixnum] :port The port on which to connect, to the destination host
# @option params [Hash] :query Default query; appended to the 'scheme://host:port/path/' in the form of '?key=value'. Will only be used if params[:query] is not supplied to Connection#request
# @option params [String] :scheme The protocol; 'https' causes OpenSSL to be used
# @option params [String] :proxy Proxy server; e.g. 'http://myproxy.com:8888'
# @option params [Fixnum] :retry_limit Set how many times we'll retry a failed request. (Default 4)
# @option params [Class] :instrumentor Responds to #instrument as in ActiveSupport::Notifications
# @option params [String] :instrumentor_name Name prefix for #instrument events. Defaults to 'excon'