Add support for internal ( fragment ) links using [bw_link] about oik HOT 3 CLOSED

The solution delivered in Feb 2016 only supports links where the fragment is just part of the link
e.g. [bw_link example.com/page#fragment] or [bw_link example.com/page/#fragment]
and not where it's intended to be a link to somewhere else on the page
e.g. [bw_link #fragment].

The current implementation on some sites appears a bit flaky, with scrolling to the selected ID only working on a tablet. This observation needs verifying.

The solution should support at least some of the techniques documented in https://en.m.wikipedia.org/wiki/Fragment_identifier

from oik.

The code's been updated to provide better support when linking to a specified domain and when using #fragment on its own.
Tests have been implemented for both without fragments - see below - and with.

Notes:

• When we link to somewhere in the current domain we don't check that the permalink exists
• We no longer support links to child pages
• $domain may not include the scheme... as it's stripped in bw_get_domain

from oik.

It would also be nice to be able to automatically generate nice link text and title when using #fragment.
to support something like this.

[bw_link "#This fragment"]
[bw_link "#That fragment"]
...
[div id="This fragment"]
<h3>This fragment</h3>
[ediv]
[div id="That fragment"]
<h3>That fragment</h3>
[ediv]

from oik.