Changing refs from /usr/bin to /usr/local/bin

Thanks to @jaredfolkins for the feedback

Test that the host header forwarding on proxy

Support for placeholders in fastcgi env vars.

This is inconsistent with the other directives, but import is a special
case and frankly the behavior of import shouldn't change depending
on the directory from which you run caddy. Breaking change but I think
it's for the better, and best to do it now before 1.0.

Also see
https://forum.caddyserver.com/t/caddy-0-9-beta-version-available-updated-beta-2/146/29?u=matt
which has another account of strange proxy behavior; I think this
resolves that.

Also a few little formatting changes and comments.

If we listen on 127.0.0.1:80 for `localhost` but :80 for everything else,
then a hostname in the hosts file that resolves to 127.0.0.1 will be
served on :80 (unless the bind directive is used) but the OS will use
the socket listening at 127.0.0.1:80, thus giving a "No such site" error
even though the site is there, but it's on the other listener at :80.

Two ways to fix this: 1) Leave as-is and require the user to set "bind
127.0.0.1" in their Caddyfile for all sites that are resolved in the
hosts file, or 2) Take out this special case and let localhost sites
listen on :80 (unless the user changes that with the bind directive, of
course). Having localhost bind to any interface is a little annoying
(unsettling?) but probably best in the long run.

https://forum.caddyserver.com/t/wildcard-virtual-domains-with-wildcard-roots/221/9?u=matt

Add filemanager directive

Fix go get url

Fixes #904

OnStartup and OnShutdown callbacks now run as part of restarts, too.
The startup and shutdown directives only run their commands NOT as part
of restarts, as before. Some middleware that use OnStartup may need to
switch to OnFirstStartup and implement OnFinalShutdown to do any cleanup
as needed.

Minor refactor for rewrite.

* rewrite: fix new case
- added new test case and solution
- fix test case on rewrite_test

* replacer: change to table test

Fix missed if_op refactor. Ensure with tests.

* checkpoint

* Added RequestMatcher interface. Extract 'if' condition into a RequestMatcher.

* Added tests for IfMatcher

* Minor refactors

* Refactors

* Use if_op

* conform with new 0.9 beta function changes.

Also fixed a few typos and renamed caddyfile.ServerBlocks() to
caddyfile.Parse().

Refactoring to remove lint warnings