Add plugin handler.

- use: to add plugin into pgrest.
- init-plugins: initialize used plugins.
- invoke-hook: execute hook function of used plugins.
seperate mk-pgparam to 2 middlewares.

- pgparam-init: pgparam init.
- pgparam-session: save cookie in pgparam.
- also remove passport relevant codes.
remove passportjs relelvant codes.
fix typo.
let pgrest.use is a alias of pgrest.plugin.use.
tweak hooks lookup algorithm.

- hooks are exported functions of a module with special prefix (prehook-, posthook-).
Add 4 hooks in cli.

- posthook-pgrest-create-plx
- posthook-express-create-app
- prehook-pgrest-mount-default
- posthook-pgrest-create-server
Let plugins can hook cli argv, configuration processing.
fix plugins are always active if a user deactive them.
rename hooks name of cli.
Add cli posthook of http server listen.
express as peerDep so pgrest-passport can have it
check a plugin is valid in use().
rename captialize to dash2camel.
add test to check a plugin must have isactive function.
remove socket.io from pgrest

move to pgrest-websocket plugin
Merge pull request #51 from poga/feature/plugin-mechanism-experimental

remove socket.io from pgrest
preparing for 0.1.0
More authors
regen package