Improved subjects in Controller and Routing chapter

[jreklund]

Another day, another chapter. Now I went over "Controllers and Routing" chapter of the user guide.

• Tabs to space. Added tables. etc
• Added additional information to Controllers about PSR-4
• IncomingRequest Class - Class Reference from parent where incorrect
• HTTP Messages - Methods where incorrect and incomplete
• Request Class - Methods where incomplete
• URI Routing - "Method" referenced as "function"
• getVar referenced as it only got two parameters, there are a third one.

What is left to do:

IncomingRequest Class
    php:method (missing functions, and checking current ones)
Content Negotiation
    php:class
        php:method (all, as it non existing)

Demo at:
https://codeigniter.johaneklund.com/userguide/master/incoming/controllers.html

Checklist:

• Securely signed commits
• User guide updated
• Conforms to style guide