Links export correctly; blocks do not

I've tested this with both the built in `rremark` link type and local definitions.

- `rremark:foo` correctly appears red in Org Mode, and correctly exports to LaTeX as `{\color{red}\bfseries foo: foo( Aim for success! )}` . I don't know if this syntax allows for changing the keyword arguments.

- `#+begin_rremark ... #+end_rremark` blocks are highlighted in Org Mode (so it definitely recognises them), but simply exports to LaTeX as `\begin{rremark} ... \end{rremark}`. It also seems to ignore the block name and keyword arguments.