1. Remove function `get_att_val`:
That function uses `eval` to set default values for bash variables.
Because it is very dangerous to use `eval` (someone call it the plague of shell scripting), I'd like to use the bash builtin to do that.
2. Double quote all variables to avoid unexpected expansion when using it.
it's not conflicted with shadowsocks-python now. users can install both python and libev
ports of shaowsocks now. but they should migrate their old configuration file from
/etc/shadowsocks/config.json to /etc/shadowsocks-libev/config.json