hiqdev/php-billing also uses Hoa

Enhanced Context to access offsets as object properties.

This commit enhances Context behavior so the following context

```php
$context = new Context();...

Address hoaproject/Central#81.

Define minimal supported version of PHP needed into composer.json

Address hoaproject/Central#70

An array dimension is of type `array`. However, PHP has array-like
types, like the `ArrayAccess`...

Logical operators are commonly left-associative, and so it is in
PHP. This patch change the asso...

It was only possible to call dimensions on a variable, so:

x.y[7].z(42)

but it was not pos...

This method was scheduled to be deleted in 2.x.

With this patch, the auto laziness is computed when the name changes,
and no longer only on the ...

`hoa/protocol` was required by `hoa/compiler`, but it's better to have
it as an explicit depende...

The core is being splitted into several libraries. `Hoa\Exception` is
one of them.

Please see the test: It is self-expressing.

It allows to check if a subject matches a regex:

subject matches "foo|bar" or another_subje...

If we have the rule `true`, the interpreter will compute a boolean value
`true` for the expressi...

Thanks @osaris for pointing this out :-).