merge(third_party/cgit): Import at master of 2020-01-11

Imported commit '723dc8fbcb' as
'third_party/cgit'.

third_party/cgit/README

@@ -0,0 +1,99 @@
+cgit - CGI for Git
+==================
+
+This is an attempt to create a fast web interface for the Git SCM, using a
+built-in cache to decrease server I/O pressure.
+
+Installation
+------------
+
+Building cgit involves building a proper version of Git. How to do this
+depends on how you obtained the cgit sources:
+
+a) If you're working in a cloned cgit repository, you first need to
+initialize and update the Git submodule:
+
+    $ git submodule init     # register the Git submodule in .git/config
+    $ $EDITOR .git/config    # if you want to specify a different url for git
+    $ git submodule update   # clone/fetch and checkout correct git version
+
+b) If you're building from a cgit tarball, you can download a proper git
+version like this:
+
+    $ make get-git
+
+When either a) or b) has been performed, you can build and install cgit like
+this:
+
+    $ make
+    $ sudo make install
+
+This will install `cgit.cgi` and `cgit.css` into `/var/www/htdocs/cgit`. You
+can configure this location (and a few other things) by providing a `cgit.conf`
+file (see the Makefile for details).
+
+If you'd like to compile without Lua support, you may use:
+
+    $ make NO_LUA=1
+
+And if you'd like to specify a Lua implementation, you may use:
+
+    $ make LUA_PKGCONFIG=lua5.1
+
+If this is not specified, the Lua implementation will be auto-detected,
+preferring LuaJIT if many are present. Acceptable values are generally "lua",
+"luajit", "lua5.1", and "lua5.2".
+
+
+Dependencies
+------------
+
+* libzip
+* libcrypto (OpenSSL)
+* libssl (OpenSSL)
+* optional: luajit or lua, most reliably used when pkg-config is available
+
+Apache configuration
+--------------------
+
+A new `Directory` section must probably be added for cgit, possibly something
+like this:
+
+    <Directory "/var/www/htdocs/cgit/">
+        AllowOverride None
+        Options +ExecCGI
+        Order allow,deny
+        Allow from all
+    </Directory>
+
+
+Runtime configuration
+---------------------
+
+The file `/etc/cgitrc` is read by cgit before handling a request. In addition
+to runtime parameters, this file may also contain a list of repositories
+displayed by cgit (see `cgitrc.5.txt` for further details).
+
+The cache
+---------
+
+When cgit is invoked it looks for a cache file matching the request and
+returns it to the client. If no such cache file exists (or if it has expired),
+the content for the request is written into the proper cache file before the
+file is returned.
+
+If the cache file has expired but cgit is unable to obtain a lock for it, the
+stale cache file is returned to the client. This is done to favour page
+throughput over page freshness.
+
+The generated content contains the complete response to the client, including
+the HTTP headers `Modified` and `Expires`.
+
+Online presence
+---------------
+
+* The cgit homepage is hosted by cgit at <https://git.zx2c4.com/cgit/about/>
+
+* Patches, bug reports, discussions and support should go to the cgit
+  mailing list: <cgit@lists.zx2c4.com>. To sign up, visit
+  <https://lists.zx2c4.com/mailman/listinfo/cgit>