updating to work with grunt v0.4.0rc5.

this PR is far from complete but there are things that are going to need to be discussed so creating it as a placeholder that eventually will be merge-able. commits will be squashed at that point.

### Changes

- [x] each target will have exactly one output file. set by `archive` option.
- [x] file's `dest` refers to the internal path within the output file.
- [x] remove `cwd`, `flatten`, `rootDir`, `minimatch` options; can be controlled by grunt multi-task config modifiers now.
- [x] replace `node-tar` with `archiver`; cuts down on code greatly.
- [x] new examples and docs.
- [ ] new tests that check integration with grunt multi-task config modifiers. (ie cwd, flatten, expand, etc)

### Current Issues

- [ ] with new flow, `gzip` becomes useless since one output file per target.

### Testing/Install Now

```shell
npm install ctalkington/grunt-contrib-compress#patch5 // shorthand node >= v0.8.17
npm install https://github.com/ctalkington/grunt-contrib-compress/archive/patch5.tar.gz
```