Fix issues with the router

[ghost]

Fix #1938, #1961; reverts #1078.

Bonuses:

• Relaxed the requirement for the route to start with a slash (see https://github.com/phalcon/cphalcon/blob/1.3.0/ext/kernel/framework/router.c#L175 and @xboston 's test)
• Merge slashes when prefix ends and pattern starts with a slash ($this->setPrefix('/test-class/')->add('/test/{id:\d}') will result in /test-class/test/1, not /test-class//test/1)

[phalcon]

Could you please rebase this?

[ghost]

Done.