Use latest roxygen2 tags for R6 documentation

[schloerke]

Calling devtools::document() produces many warnings.

Currently:

Warning: [./httpuv/R/httpuv.R:389] undocumented R6 methods: `initialize`, `onMessage`, `onClose`, `send`, `close`
Warning: [./httpuv/R/httpuv.R:389] undocumented R6 fields: `handle`, `messageCallbacks`, `closeCallbacks`, `request`
Warning: [./httpuv/R/httpuv.R:392] argument `handle` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/httpuv.R:392] argument `req` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/httpuv.R:396] argument `func` undocumented for R6 method `onMessage()`
Warning: [./httpuv/R/httpuv.R:399] argument `func` undocumented for R6 method `onClose()`
Warning: [./httpuv/R/httpuv.R:402] argument `message` undocumented for R6 method `send()`
Warning: [./httpuv/R/httpuv.R:413] argument `code` undocumented for R6 method `close()`
Warning: [./httpuv/R/httpuv.R:413] argument `reason` undocumented for R6 method `close()`
Warning: [./httpuv/R/server.R:49] undocumented R6 methods: `stop`, `isRunning`, `getStaticPaths`, `setStaticPath`, `removeStaticPath`, ...
Warning: [./httpuv/R/server.R:71] argument `...` undocumented for R6 method `setStaticPath()`
Warning: [./httpuv/R/server.R:71] argument `.list` undocumented for R6 method `setStaticPath()`
Warning: [./httpuv/R/server.R:78] argument `path` undocumented for R6 method `removeStaticPath()`
Warning: [./httpuv/R/server.R:89] argument `...` undocumented for R6 method `setStaticPathOption()`
Warning: [./httpuv/R/server.R:89] argument `.list` undocumented for R6 method `setStaticPathOption()`
Warning: [./httpuv/R/server.R:160] undocumented R6 methods: `initialize`, `getHost`, `getPort`
Warning: [./httpuv/R/server.R:164] argument `host` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:164] argument `port` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:164] argument `app` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:164] argument `quiet` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:251] undocumented R6 methods: `initialize`, `getName`, `getMask`
Warning: [./httpuv/R/server.R:255] argument `name` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:255] argument `mask` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:255] argument `app` undocumented for R6 method `initialize()`
Warning: [./httpuv/R/server.R:255] argument `quiet` undocumented for R6 method `initialize()`