Allow escaped newlines before first option

[theY4Kman]

The current parser only allows escaped newlines after each option, but not before the first option. This means it can handle rules like these:

alert tcp $HOME_NET any -> $EXTERNAL_NET any ( msg:"Stuff!"; \\
  content:"abc"; )

alert tcp $HOME_NET any -> $EXTERNAL_NET any ( msg:"Stuff!"; \\
  content:"abc"; \\
)

alert tcp $HOME_NET any -> $EXTERNAL_NET any ( msg:"Stuff!"; \\
  \\
  \\
  content:"abc"; \\
)

But not this:

alert tcp $HOME_NET any -> $EXTERNAL_NET any ( \\
  msg:"Stuff!"; \\
  content:"abc"; \\
)

This PR allows newlines to be written before the first option.

Additionally, this PR allows newlines at the end of the file, which apparently have never worked, or #2 broke it.