add docs for ngx_http_sysguard_module

Chinese and English version.

Signed-off-by: Paul Yang(InfoHunter) <paulyang.inf@gmail.com>
add docs for ngx_http_upstream_dynamic_module

English and Chinese versions.

Signed-off-by: Paul Yang(InfoHunter) <paulyang.inf@gmail.com>
fix grammar error in docs

Signed-off-by: Paul Yang(InfoHunter) <paulyang.inf@gmail.com>
Fix doc errors for sysguard and upstream_dynamic

Signed-off-by: Paul Yang(InfoHunter) <paulyang.inf@gmail.com>
Merge pull request #508 from InfoHunter/master

add docs for sysguard module and upstream_dynamic module
bugfix: ngx_http_upstream_init_process will cause coredump while not have http block.
Feature: the "gzip_clear_etag" directive.
Merge pull request #515 from taoyuanyuan/random

bugfix: ngx_http_upstream_init_process will cause coredump
Merge pull request #514 from taoyuanyuan/etag

Feature: the "gzip_clear_etag" directive.
add doc for the "gzip_clear_etag" directive.
Merge pull request #516 from taoyuanyuan/doc

add doc for the "gzip_clear_etag" directive.
Merge pull request #3 from alibaba/master

Update from origin