Run using child_process `spawn` rather than `exec`

[mhh]

This PR modifies gulp-msbuild so that it will execute MSBuild using child_process.spawn instead of child_process.exec.

There are a few benefits to doing so:

• MSBuild's console message coloring is preserved (see https://groups.google.com/forum/#!topic/nodejs/t8dPnfqVl6U for background)
• The maxBuffer option is no longer needed
• Arguments supplied to MSBuild no longer need to be escaped

[mhh]

@redwards1966 I just read about the problem you reported in issue #24 -- I'd be curious to know if xbuild still works for you when using this branch?

[hoffi]

Really like your solution. Thanks!

I have tried the example from #24 using this solution with xbuild and it worked for me.

But if the build fails and i have turned errorOnFail on i get this at the end:

[19:06:24] Build failed with code 1!
[19:06:24] 'default' errored after 268 ms
Error: [object Object]
    at formatError (/usr/local/lib/node_modules/gulp/bin/gulp.js:169:10)
    at Gulp.<anonymous> (/usr/local/lib/node_modules/gulp/bin/gulp.js:195:15)
    at emitOne (events.js:77:13)
    at Gulp.emit (events.js:169:7)

I think this is because of line 41 in msbuild-runner.js because gulp expects an error object as callback argument.

[mhh]

Thank you for the feedback, @hoffi. Commit 31ab100 should address that problem.

[hoffi]

Looks good to me. Thank you very much :+1: