Pyppeteer

* Support `raf` and `mutation` polling for `waitFor*` methods
* Add `Page.coverage` to support JS and CSS coverage
* Add XPath support with `Page.xpath`, `Frame.xpath`, and `ElementHandle.xpath`
* Add `Target.createCDPSession` to work with raw Devtools Protocol
* Change `Frame.executionContext` from property to coroutine
* Add `ignoreDefaultArgs` option to `pyppeteer.launch`
* Add `handleSIGINT`/`handleSIGTERM`/`handleSIGHUP` options to `pyppeteer.launch`
* Add `Page.setDefaultNavigationTimeout` method
* `Page.waitFor*` methods accept `JSHandle` as argument
* Implement `Frame.content` and `Frame.setContent` methods
* `page.tracing.start` accepts custom tracing categories option
* Add `Browser.process` property
* Add `Request.frame` property

* `pyppeteer.launch()` is now **coroutine**
* Implement `connect` function
* `PYPPETEER_DOWNLOAD_HOST` env variable specifies host part of URL to download chromium
* Rename `setRequestInterceptionEnable` to `setRequestInterception`
* Rename `Page.getMetrics` to `Page.metrics`
* Implement `Browser.pages` to access all pages
* Add `Target` class and some new method on Browser
* Add `ElementHandle.querySelector` and `ElementHandle.querySelectorAll`
* Refactor NavigatorWatcher
* add `documentloaded`, `networkidle0`, and `networkidle2` options
* `Request.abort` accepts error code
* `addScriptTag` and `addStyleTag` return `ElementHandle`
* Add `force_expr` option to `evaluate` method
* `Page.select` returns selected values
* Add `pyppeteer.version` and `pyppeteer.version_info`

* BugFix:
* Do not change original options dictionary
* `Page.frames`
* `Page.queryObjects`
* `Page.exposeFunction`
* Request interception
* Console API
* websocket error on closing browser (24)

* Remove `ElementHandle.evaluate`
* Remove `ElementHandle.attribute`
* Deprecate `Page.plainText`
* Deprecate `Page.injectFile`
* Add `Page.querySelectorAllEval`
* Add `Page.select` and `Page.type`
* Add `ElementHandle.boundingBox` and `ElementHandle.screenshot`
* Add `ElementHandle.focus`, `ElementHandle.type`, and `ElementHandle.press`
* Add `getMetrics` method
* Add `offlineMode`

* Add `$PYPPETEER_NO_PROGRESS_BAR` environment variable
* `pyppeteer.defaultArgs` now accepts that help infer chromium command-line flags.
* `pyppeteer.launch()` argument `ignoreDefaultArgs` now accepts a list of flags to ignore.
* `Page.type()` now supports typing emoji
* `Page.pdf()` accepts a new argument `preferCSSPageSize`
* Add new option `defaultViewport` to `launch()` and `connect()`
* Add `BrowserContext.pages()` method

* Fix miss-spelled methods and functions
* Change `Browser.isIncognite` to `Browser.isIncognito`
* Change `Browser.createIncogniteBrowserContext` to `Browser.createIncognitoBrowserContext`
* Change `chromium_excutable` to `chromium_executable`
* Remove `craete` function in `page.py`