And move emqx app back to root level
After realising the challenges of developing plugins in standalone
rebar projects. it is perhaps more smooth to keep using emqx as
a rebar dependency
- Add dialyzer for code analysis
- Correct all the module type declarations
- Use `-type()` to declaration a type instead of `-opaque`
(It is advantageous to the code dialyzer)
BROKEN CHANGES:
- Add a ?DEFAULT_SUBOPTS for emqx_broker:subscribe/1,2,3
- Remove the needless internal function `emqx_vm:port_info(PortTerm, Keys)`
Zaiming Shi