[WIP] Add Stack Middlewares and example

[jeromemacias]

• Add microrest stack middleware
• Add demo using microrest stack middleware
• Use Cors middleware to the stack demo
• Add microrest doc middleware
• Use Silex webprofiler and logger, expose result to /_microrest_profiler url and specific log file
• Add tests

[fzaninotto]

Fine by me. What's left for RFR?