Add gyp.js (https://github.com/indutny/gyp.js) support

See issue #960

Added initial `gyp.js` support with --gypjs command line option.
Environment variable `npm_config_gypjs` also turns this option on.

Update configure and build usage strings depending on `npm_config_gypjs`
environment variable

Author: pmed

README.md

@@ -181,6 +181,7 @@ Command Options
 | `--python=$path`                  | Set path to the python (2) binary
 | `--msvs_version=$version`         | Set Visual Studio version (win)
 | `--solution=$solution`            | Set Visual Studio Solution version (win)
+| `--gypjs`                         | Use gyp.js instead of gyp
 
 
 License

gyp/buildbot/buildbot_run.py

@@ -1,5 +1,5 @@
-@rem Copyright (c) 2009 Google Inc. All rights reserved.
-@rem Use of this source code is governed by a BSD-style license that can be
-@rem found in the LICENSE file.
-
-@python "%~dp0gyp_main.py" %*
+@rem Copyright (c) 2009 Google Inc. All rights reserved.
+@rem Use of this source code is governed by a BSD-style license that can be
+@rem found in the LICENSE file.
+
+@python "%~dp0gyp_main.py" %*