Extend tls client auth

Caddyfile parameter "clients" of "tls" henceforth accepts a special
first modifier. It is one of, and effects:

 * request         = tls.RequestClientCert
 * require         = tls.RequireAnyClientCert
 * verify_if_given = tls.VerifyClientCertIfGiven
 * (none)          = tls.RequireAndVerifyClientCert

The use-case for this is as follows: A middleware would serve items to the
public, but if a certificate were given the middleware would permit file
manipulation.

And, in a different plugin such as a forum or blog, not verifying a client
cert would be nice for registration: said blog would subsequently only
compare the SPKI of a client certificate.

No need to have this in every plugin. And, even in flat filesystems
filenames with dots and slashes are best avoided.

For example, a HTTP POST should not be answered with StatusOK,
and a response to HTTP OPTIONS should not carry any contents.

browse: Dropped LinkedPath and updated browse template

As discussed with @mholt I have dropped the old LinkedPath function and
replaced it within the browse template with the new BreadcrumbMap
function. Visually it looks exactly the same as before, now the template
functionality is just more powerful.
Signed-off-by: Thomas Boerger <tboerger@suse.de>

Added breadcrumb map function to browse

In order to being able to really build a custom template for the browse
directive I have added another function to build even custom breadcrumb
paths. The other function `LinkedPath` is not that easy styleable as
this map function. That way we are able to build the breadcrumb path
matching different CSS frameworks like Bootstrap.
Signed-off-by: Thomas Boerger <thomas@webhippie.de>

Added "go up" link to browse template

In order to have directly a link within the browse listing I have added
a link to the top of the table to get one level up in the tree. Added
that after a chat with @mholt.
Signed-off-by: Thomas Boerger <thomas@webhippie.de>

To be consistent with 3faad41b and c64cf218

http.CloseNotifier implementation for http.ResponseWriter wrapper

Signed-off-by: Tw <tw19881113@gmail.com>

Nuke pre-generation.  This may come back in the form of a more general
caching layer at some later stage.

Nuke index generation.  This should likely be rethought and re-implemented.

Caddy recovers panics that occur in the middleware stack so this is not a risk to process termination. This way is also preferable to hiding the error. See https://github.com/mholt/caddy/commit/3faad41b437c48cea37863123fab425169bc0c6e#commitcomment-17035158

Easier parallelism and more control over platforms we build for, but
more importantly, we can do parallel builds using the build script which
properly embeds version information into the binaries. We also produce
the archive files ourselves and in parallel rather than using external
tar and zip commands.

Flush every 250ms. This should keep latency somewhat low but there is
still buffering; maybe in the future we can make this configurable.

Handle host names case insensitively.

RFC 3986 3.2.2: The host subcomponent is case-insensitive.

Extract restartInProc to its own file

Also testing commit signing again, different email this time.

This will help build server perform builds with copy of repo in a folder
outside the original git repo folder. Also testing signed commits on
GitHub.

Rename EC256,EC384 to P256,P384