Support indented/inline line magics

Line magics can appear just about anywhere:

however, the whitespace of code generated by hy is not preserved:

``` hylang
(if True
  %ls
)
```

``` python

  File "<ipython-input-17-b11eae11951f>", line 1
    (%ls if True else None)
     ^
SyntaxError: invalid syntax
```

likely a macro is needed?
