Automatic links to ClassNames.

DocFormatter will now look for names like Ext.form.Field and convert
them automatically to links.  The same works for method names, when
written like MyClass#method.

Only links to existing classes are created.  So that when there is
Foo.Bar in method description but the Foo.Bar class doesn't exists
(not included to documentation), then no link is created.

Additionally a DocFormatter instance is now created only once per
the creation of one documentation page, and then passed on to all
the classes taking part of page creation.  So, no more repeated
initialization code.