No tags for FFI calls

```
foreign import ccall unsafe "HsRead" c_Read :: ....
```
Should generate `c_Read` entry in a hask tags file.  Note that `c_Read` can also be placed in a new line:
```
foreign import ccall usafe "HsRead"
  c_Read :: ...
```

To add the actual c function `HsRead` one can run `ctags -a **/*.c`.