Heroku supports PHP. Fix link.

Heroku PHP support is now GA.
https://blog.heroku.com/archives/2014/7/15/the_new_php_on_heroku_now_generally_available
Merge pull request #420 from iakio/patch-1

Heroku supports PHP. Fix link.
Fix menu links for "welcome" anchors.

In the `index.html`, `{{ welcome_content |markdownify }}` generates name
attributes for header tags like "my-title", whereas `{{ post.content }}`
generates name attributes like "my_title".

This fixes the links for only the welcome menu items so that the anchors
in the menu match the different name format.
Change branch names from "master" to "gh-pages".
Merge pull request #423 from jwpage/welcome_anchors

Fix menu links for "welcome" anchors.
Merge pull request #424 from jwpage/contributing_master

Change branch names from "master" to "gh-pages".