…ndows

Using `target_arch` in addon.gypi to link against Node.js library.
This variable was written into build/config.gypi on the `configure` stage.

Do not copy node.lib into node_root_dir/Release or node_root_dir/Debug
on Windows, link it from node_root_dir/target_arch directory.

Removed unused copyNodeLib() function
Removed unused `copy_dev_lib` variable introduced in commit
@84d24189735e19350a93aaf9f6a327bb4c52349e

Set path to node lib in `$(Configuration)` dir when `--nodedir` option is
supplied, otherwise use value of `target_arch` variable.

See issue nodejs#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.

Set `npm_config_gypjs` env variable if `--gypjs` command-line option
was set to affect usage text for `configure` and `build` commands.

Update usage strings if `--gypjs` command-line option was supplied

Trying to load gyp.js module only if --gypjs command-line option was supplied.