@Controller -> @RestController in docs

Fixes gh-652
/etc/bash_completion.d -> something else

I preferred /etc/bash_completion.d (since it mirrors the actual
preferred deployment of the scripts on my OS). Maybe the MacBoys
have a different point of view? Anyway the docs now point to the
actual script location.

Fixes gh-651
@Controller -> @RestController in README

Fixes gh-652 some more
Fixed minor mistakes

* your -> you're
* ask a questions -> ask a question

Fixes gh-653
Add enabled flag to RegistrationBean

Default to true but allow user to switch off a @Bean of type
Filter (for example) by wrapping it in a disabled registration.

Fixes gh-655
Minor fixes in the docs