Stop recommending `and`/`or` over `&&`/`||`

The coding guidelines suggest using `and` and `or` over `&&`
and `||`. Frankly I don't think this is a good idea. The
precedence rules for `and` and `or` are so weird, they will
cause lots of confusion and edge cases.

To illustrate this, look at the following example ([from logical
operators][0]):

    $x = false or true;

What do you expect the value of `$x` to be? It's `false`, because
`or` has lower precedence than `=`. So while you expected the
expression to be:

    $x = (false or true);

It is in fact:

    ($x = false) or true;

Stop using `and`/`or` as logical operators. They were designed
for flow control.

[0]: http://php.net/manual/en/language.operators.logical.php
Merge pull request #290 from igorw-forks/patch-1

Stop recommending `and`/`or` over `&&`/`||`
Add note to docs about registering providers at run-time.
Update docs with composer install instructions.