Decide about complicated url expansions

[adamwolf]

GitHub's url expansion behavior is complicated! I introduced a basic form in #23, but while doing that, I made a list of things that expanded and didn't expand, and what they expanded to.

I was not able to find any documentation for any of this.

• http://www.github.com/adamwolf/issue-expander/issues/23 does NOT expand

• http://github.com/adamwolf/issue-expander/issues/23 does NOT expand

• https://www.github.com/adamwolf/issue-expander/issues/23 does NOT expand

• https://github.com/adamwolf/issue-expander/issues/#23 does NOT expand

• https://github.com/adamwolf/issue-expander/pull/#23 does NOT expand

• https://github.com/adamwolf/issue-expander/issue/23 does NOT expand

• https://github.com/adamwolf/issue-expander/pulls/23 does NOT expand

• https://en.github.com/adamwolf/issue-expander/issues/23 does NOT expand

• https://github.blog/adamwolf/issue-expander/issues/23 does NOT expand

• https://github.org/adamwolf/issue-expander/issues/23 does NOT expand

• https://github.org/adamwolf/issue-expander/pull/23 does NOT expand

• https://github.com/adamwolf/issue-expander/pull/23foo does not expand

• Detect basic url references #23. expands and puts a . after the link

• Detect basic url references #23 expands and eats the -

• doubling up the site, like this Detect basic url references #23 only expands it once?!

• https://github.com/adamwolf/issue-expander/pull/23#foo#bar does expand and eats the #bar!

• Detect basic url references #23 does expand

• Detect basic url references #23 does expand

• Detect basic url references #23 (comment) does expand WITH EXTRA TEXT!?!?!