handle path params with prefixes and suffixes

[jaswdr]

In current implementation if you have a path parameter with some prefix or suffix the path processor doesn't extract the values correctly, see some examples:

/foo_{var}
/{var}_foo
/foo_{var}_bar

This patch handle those cases using regexp to correctly extract values.

[emicklei]

i am worried about the performance impact of this change. Creating and executing regexp can be expensive.

[jaswdr]

@emicklei ack, I used now strings indexes like the previous code, please let me now if this feel better

[jaswdr]

ping @emicklei

[emicklei]

thank you for contributing