DDOX based docs fixes and additions

Includes four changes:

 - Adds symbol live search support using the search box in the upper left corner
 - Fixes a few links and missing resource files (posix.mak)
 - Automatically calls "dub" to build the "dpl-docs" tool, so that it is automatically kept up to date
 - Adds a small link to the DDOX docs in the main table of contents

Also requires https://github.com/D-Programming-Language/tools/pull/102 to actually show the search box