handles optional segments in uri generation

[pine3ree]

Quick fix to handle routes defined with path like:

//...
'name' => 'blog/post',
'path' => '/blog/post[/{action:index|recent}[/{page:\d+}[/optional-{extra}]]]',
//...

$urlHelper('blog/post');

// assume that current matching route has action=index and page=3

// w/o fix  => blog/post[/index[/3[/optional-{extra}]]]  
// with fix => blog/post/index/3

• TODO: add unit test case ***DONE
• ALT: use slim-3 method (leveraging fastroute std route parser) for uri generation? ***NO
• throw exception if substituted optional segment lives inside an unsubstituted optional segment? ***DONE
• use regex for argument matching instead of strpos? (strpos is faster and should be enough to match opening curly brackets for acceptable fast-route paths)