Sphinx 1.4 comes with sphinx.ext.githubpages extension, whose sole
feature is to put a .nojekyll file in the root directory of the built
HTML so that GitHub Pages doesn't make bad assumptions.

Sphinx 1.3 is packaged in Ubuntu 14, however, and doesn't ship with the
extension, so vendor it.

RTL_RUN_ONCE and suseconds_t were undefined when building with CMake and
MinGW-W64. We conditionally define those if build with MS Visual Studio,
but we should conditionally define them if building on MS Windows, no
matter which compiler.

The deprecated binary subtype 2 has a redundant length prefix at the
start of the data, check it agrees with the total BSON element length.

Don't replace all "()" with "(3)", and fix some <output> formatting.

Mallard lines like "Optional <code>bson_t</code>. Might be NULL." was
output as:

Optional
.B bson_t
. Might be NULL.

Groff misinterprets, and truncates at the first period. Escape the dot:

Optional
.B bson_t
\[char46] Might be NULL.