Fix buttons shortcode

[robyngit]

The buttons created in #102 look great! I noticed a couple of issues:

1. some of the page references are not creating valid links. For example, in http://localhost:1313/goals/artisanal-fishing-opportunities/ the "practical guidance" button leads to a 404. I think this is because the location of the goal guidance pages changed. If we use hugo's ref function to resolve links, then these issues will be caught before the page is successfully built. It also allows content editors to link to pages with or without a file extension, with or without an anchor, and with or without the parent directory path (as long as the markdown file name is unique).

2. Internal pages are opening in a new tab because of the taget="_blank" attribute added to all the links. This should be added conditionally based on whether the link starts with http.

I fixed these issues in the very similar button shortcode, see: ee425ad

[ThomasThelen]

Partially fixed 1 in 67bcf4c
Fixed 2 in 67eb159

If time permits I'll go through and use ref for the links

[robyngit]

Fixed this in #126 by formatting the button shortcode such that multiple buttons can be added in a row. Buttons shortcode no longer needed.