Configuration.

Added support for configuration, for setting default values where
possible to alter the behavior of all request builders if desired.

For example, in grails-app/conf/Config.groovy:

requestbuilder {
    connectionTimeout = 30000
    readTimeout = 60000
    contentType = "application/json"
    accept = "application/json"
    debug = true
    ignoreInvalidSSL = true
    chunkSize = 128
    encodeGzip = true
}

Omitting any field will assume the default behavior already present in
the current versio nof RequestBuilder.