Change doc examples to be checked at compile time

[workhorsy]

Change this:

/++
Adds two numbers and retuns the result

Params:
 a = First value to add
 b = Second value to add

Examples:
----
int z = add(1, 4);
----
+/

int add(int a, int b) {
	return a + b;
}

To this:

/++
Adds two numbers and retuns the result

Params:
 a = First value to add
 b = Second value to add
+/

int add(int a, int b) {
	return a + b;
}

///
unittest {
	int z = add(1, 4) ;
}

The example in the first docstring will not be verified. We can move it to a unittest and use /// to tell ddoc that it is the example.