Change _search to use HTTP GET

- This makes it so that searches can be linked and refreshed
Create page if no match is found when using _go

This was a usability issue pointed out by a non-technical user.
There seemed to be no obvious way to create new pages. This was
the suggested solution and the easiest to implement.
Document added mod_proxy_html setting in README

Add a mod_proxy_html configuration directive to insert a DOCTYPE string.
Merge pull request #398 from wjv/wjv

Document added mod_proxy_html setting in README
Merge pull request #397 from joehillen/_go-createPage

Create page if no match is found when using _go
Merge pull request #396 from joehillen/_search-GET

Change _search to use HTTP GET
Merge remote-tracking branch 'upstream/master'