Enable route paths as symbol and optional leading '/'

So far, all routes must be strings and the first character has to be slash -
'/'.

This commit enables the following:
- routes can be symbols too
- when path is string, leading slash character is optional

@pachacamac, if you like this change, what are your suggestions about updating
the README? I didn't want to add new routes just to show symbols can be used
for paths.. maybe we should change just one of the simpler routes (e.g.
'/info') to symbol, just to show it's possible.
Feedback appreciated!