Dash handling

[astik]

Hi,

I would be perfect to handle the dash syntax :

- (dash)
    A dash indicates that no substitution should be performed (the existing path is passed through untouched). This is used when a flag (see below) needs to be applied without changing the path.

It would be possible to write something like this :

'^/data/(.*)$ - [L]',

instead of

'^/data/(.*)$ /data/$1 [L]'

[tinganho]

@astik sound useful. Do you mind land a PR?�