Modify context variable names and write docs (#133)

Author: donny-dont

lib/browser_client.dart

@@ -23,6 +23,13 @@ import 'src/response.dart';
 /// unable to directly set some headers, such as `content-length`. It is also
 /// unable to stream requests or responses; a request will only be sent and a
 /// response will only be returned once all the data is available.
+///
+/// You can control the underlying `dart:html` [HttpRequest] by adding values to
+/// [Request.context]:
+///
+/// * `"http.html.with_credentials"` is a boolean that defaults to `false`. If
+///   it's `true`, cross-site requests will include credentials such as cookies
+///   or authorization headers. See also [HttpRequest.withCredentials].
 class BrowserClient extends BaseClient {
   /// The currently active XHRs.
   ///
@@ -38,7 +45,8 @@ class BrowserClient extends BaseClient {
     _xhrs.add(xhr);
     _openHttpRequest(xhr, request.method, request.url.toString(), asynch: true);
     xhr.responseType = 'blob';
-    xhr.withCredentials = request.context['html.withCredentials'] ?? false;
+    xhr.withCredentials =
+        request.context['http.html.with_credentials'] ?? false;
     request.headers.forEach(xhr.setRequestHeader);
 
     var completer = new Completer<Response>();

lib/src/io_client.dart

@@ -15,6 +15,24 @@ import 'response.dart';
 /// A `dart:io`-based HTTP client.
 ///
 /// This is the default client when running on the command line.
+///
+/// You can control the underlying `dart:io` [HttpRequest] by adding values to
+/// [Request.context]:
+///
+/// * `"http.io.follow_redirects"` is a boolean. If it's `true` (the default)
+///   then the request will automatically follow HTTP redirects. If it's
+///   `false`, the client will need to handle redirects manually. See also
+///   [HttpClientRequest.followRedirects].
+///
+/// * `"http.io.max_redirects"` is an integer that specifies the maximum number
+///   of redirects that will be followed if `follow_redirects` is `true`. If the
+///   site redirects more than this, [send] will throw a [ClientException]. It
+///   defaults to `5`. See also [HttpClientRequest.maxRedirects].
+///
+/// * `"http.io.persistent_connection"` is a boolean. If it's `true` (the
+///   default) the client will request that the TCP connection be kept alive
+///   after the request completes. See also
+///   [HttpClientRequest.persistentConnection].
 class IOClient extends BaseClient {
   /// The underlying `dart:io` HTTP client.
   HttpClient _inner;
@@ -28,9 +46,10 @@ class IOClient extends BaseClient {
       var context = request.context;
 
       ioRequest
-        ..followRedirects = context['io.followRedirects'] ?? true
-        ..maxRedirects = context['io.maxRedirects'] ?? 5
-        ..persistentConnection = context['io.persistentConnection'] ?? true;
+        ..followRedirects = context['http.io.follow_redirects'] ?? true
+        ..maxRedirects = context['http.io.max_redirects'] ?? 5
+        ..persistentConnection =
+            context['http.io.persistent_connection'] ?? true;
       request.headers.forEach((name, value) {
         ioRequest.headers.set(name, value);
       });