Support c2hs (at least partially)

It'd be really cool if stylish-haskell could support files that uses c2hs.
I'm mainly looking for support for making imports stylish.

The `.chs` files include lines like

``` haskell
{#pointer *channel as ^ newtype#}
```

which naturally doesn't parse with a standard haskell parser.

It'd be ok if stylish-haskell only styled the imports which are not in c2hs style, and ignored or skipped the rest of the file when it encountered a c2hs import.

```
{#import Some.Haskell.Module#}
```

The issue names no repository files or tests. Start by locating the parser and import-styling entry points, then reproduce the `.chs` examples containing c2hs syntax and imports. Done means ordinary imports in `.chs` files are styled without failing on c2hs lines, while unsupported sections are skipped as agreed.

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