Maintenance updates

* Changed from "google-public-dns-a.google.com" to "dns.google"
  for the external domain change.

go.mod support

* try to use go mod download, if available.

* add go.mod and go.sum.
* in travis, set GO111MODULE=on to enable go module test.

Fix error locking

* defaultHandler.ServeHTTP will Close the client, if present.
* fix #28.
* resolve #29.

* reproduce blocking situation by limit to only 1 worker and
  simple client factory.

readme: table of content

Documentation improvements and Typo fixes

* new illustration to illustate FastCGI.
* some minor formatting and wording adjustment.

* fix typo in various code files.

* add filter example.
* add TODO in filter code to remind future development needs.

* add goreport badge.
* use <summary> and <details> on the SessonHandler example.

Various improvements

* make sure that client write to error stream if it is canceled or
  forced done.

* Update process config to static, 10 process.
* Have new SetName parameter to set basename of pid, error_log, sock
  files.
* Prevent test from basename collision.

Improve parameters mappings

* update README.md to have proper example middleware.
* demonstrate how to do REMOTE_HOST with middleware.
* demonstrate how to do REMOTE_USER with middleware.
* update Middleware documentation lines.

* fix mistake due to gofast.BasicSession changes.

* add MapRemoteHost for lookup of REMOTE_HOST.

* remove nopClient with simplier ClientFunc implementation.

Fix REQUEST_URI behaviour

* add 1.10 to test.
* use a.b.x syntax instead of a.b.

* Test REQUEST_URI for file endpoint routine in example/php.
* Fix REQUEST_URI behaviour. Fix #30.

* migrated towards local phpfpm subpackage.

* The gophpfpm library for controlling phpfpm process seems useless
  in other contexts. Migrated as local subpackage.
  Original path: https://github.com/yookoala/gophpfpm

* extract get() and post() from TestHandler() for reuse.

Add missing gofast.BasicSession to README example