Add an option to let user wrap SIP003 environment variables as normal in-line arguments

[celeron533]

Just a brainstorm

According to shadowsocks/shadowsocks-org#28 , the SIP003 arguments are delivered by environment variables:
Mandatory:
SS_REMOTE_HOST, SS_REMOTE_PORT, SS_LOCAL_HOST and SS_LOCAL_PORT
Optional:
SS_PLUGIN_OPTIONS

---

Currently, a SIP003 "compatible" plugin program must able to read and grab its Process environment variables when being launched. Equivalent to the following console commands:

1. ss-win set the environment variables

set SS_REMOTE_HOST=1.2.3.4
set SS_REMOTE_PORT=9999
set SS_LOCAL_HOST=127.0.0.2
set SS_LOCAL_PORT=33333
set SS_PLUGIN_OPTIONS=foobar

2. Then ss-win launch the plugin

start someplugin.exe

---

If user has plugins whose implementation does not following SIP003 standard, user should have a work-around to give the in-line arguments when starting the plugin program. For instance:

1. ss-win set the environment variables

set SS_REMOTE_HOST=1.2.3.4
set SS_REMOTE_PORT=9999
set SS_LOCAL_HOST=127.0.0.2
set SS_LOCAL_PORT=33333
set SS_PLUGIN_OPTIONS=foobar

2. User typed the format and pattern for the in-line arguments wrapper

-remote %SS_REMOTE_HOST%:%SS_REMOTE_PORT% -local %SS_LOCAL_HOST%:%SS_LOCAL_PORT% %SS_PLUGIN_OPTIONS%

3. Then ss-win launch the plugin by using the wrapper

start someplugin.exe -remote %SS_REMOTE_HOST%:%SS_REMOTE_PORT% -local %SS_LOCAL_HOST%:%SS_LOCAL_PORT% %SS_PLUGIN_OPTIONS%

which will be parsed into

start someplugin.exe -remote 1.2.3.4:9999 -local 127.0.0.2:33333 foobar

It should expand the selection of third-party plug-in programs.

[madeye]

The reason we use environment variable is to avoid special character issue in the command line, e.g key s like ^%$&^\/.

However, it's still worth to support CLI args in windows as some users would try to use non-SIP003 plugins.