Fix over-zealous backslash replacement

Hi,

Two things, the [first](https://github.com/jcheatham/redcarpet/commit/24127e19c97887016f492bf80a7f906ab7f6b4f8) is to fix the [current travis breakage](https://travis-ci.org/vmg/redcarpet/builds/25455860).  I wasn't sure why it started with the last build, but it seems like it was broken since the original commit, so maybe some library or gem update?  Just looks like the test just needed a \n though.

Second is for #214 ([specifically](https://github.com/vmg/redcarpet/issues/214#issuecomment-22977188)), didn't fix the original emphasis problem in that issue though, looks like that's in char_emphasis, which I'll try and take a look at that when I can.  I couldn't find any instances where the backslash needed to be escaped, but please let me know if there's some case I missed (example test would be awesome! :)

And of course please let me know if this needs something else/more to get merged.

Cheers!