Formatting inside links not working

[io12]

Formatting inside link descriptions does not parse correctly if the formatting is at the beginning or end of the link description.

Example

irb(main):017:0> Orgmode::Parser.new("[[a][~a~]]").to_html
=> "<p><a href=\"a\">~a~</a></p>\n"

The output should be "<p><a href=\"a\"><code>a</code></a></p>\n".