Implement deprecate API and deprecate APIs

[shama]

Ref: https://github.com/gruntjs/rfcs/pull/1

This implements an internal deprecations API that displays a warning in the console if one of the deprecated APIs are used.

To hide deprecation warnings, use --hide-deprecations on the CLI or grunt.option('hide-deprecations', true) in your Gruntfile.

When --stack or grunt.option('stack', true) is enabled, the deprecation warnings will print stack traces out to locate the deprecated APIs.

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The following APIs will be publicly deprecated:

• All functions on grunt.util._
• All functions on grunt.util.async
• All functions on grunt.util.namespace
• All functions on grunt.util.hooker
• grunt.util.exit
• grunt.util.toArray
• grunt.util.repeat
• All functions on grunt.file.glob
• All functions on grunt.file.minimatch
• All functions on grunt.file.findup
• grunt.file.readYAML
• grunt.file.readJSON
• All functions on grunt.event

The following APIs should be considered for deprecation although there isn't simple alternatives to point people to at this time (help?):

• grunt.util.spawn
• grunt.util.callbackify
• grunt.util.kindOf
• grunt.util.pluralize
• grunt.util.recurse

---

~~Internally Grunt still uses these deprecated APIs. We should address those deprecation warning internally first too.~~

All deprecations have now been fixed in this PR.

---

This can be released on next minor release as it is backwards compatible but only adds a new behavior. Removing the deprecated APIs will happen on the next major release.

[cowboy]

Overall, makes sense to me, Thanks, @shama for doing this. I do like the idea, though, of first implementing the warnings in verbose mode only, then in a subsequent minor release, in non-verbose mode, and then finally removing the exposed methods in a future major release. However, I'm not sure how much I care :)

[vladikoff]

Code looks good, but I will need to run this locally to make sure it deprecates. I Will try to get to that soon