Docker images now accept shell scripts, json files and certificate chain
bundles to provide configuration on a container start by placing them
into /docker-entrypoint.d/ directory.

Also the error page markup is now valid according to HTML5 specification.
All optional tags were omitted.

Currently almost all Unit object files depends on generated nxt_version.h.
This patch adds missing dependence and fixes running make with multiple
jobs.

This closes #318 issue on GitHub.

Header names and values are stored 0-terminated for ease of use in different
languages, so magic number 2 should be added to each name-value pair size.

This field was intended for MIME type lookup by file extension when serving
static files, but this use case is too narrow; only a fraction of requests
targets static content, and the URI presumably isn't rewritten.  Moreover,
current implementation uses the entire filename for MIME type lookup if the
file has no extension.

Instead of extracting filenames and extensions when parsing requests, it's
easier to obtain them right before serving static content; this behavior is
already implemented.  Thus, we can drop excessive logic from parser.