Add string method defs for ngx.config.subsystem field in ngx_lua std
Add string method defs for ngx.config.subsystem field in ngx_lua std

TODO: extend std format to allow specifying a type for a field,
and setting set of common fields for each type, so that
string methods can be defined once in main per Lua version stds
(lua5*, luajit).

xpol/luacheck,xpol/luacheck,mpeterv/luacheck,mpeterv/luacheck,xpol/luacheck,mpeterv/luacheck,linuxmaniac/luacheck,linuxmaniac/luacheck