First pass at official user-env-compile plugin

- Uses ENV and APP/ENV files
- Supports old BUILD_ENV files (which are likely in wide-use)
- Allows user's to override globals with app-specific configuration

Closes #284
Closes #683
Closes #763

Refs #503
Refs #678
Point users to upgrade guides
Fix crt/key check
Dokku pushes now happen as the dokku user, not git. Refs #796
Force install a default nginx.conf. Closes #799
Ensure ruby is installed when running the dokku-installer
Ensure makefiles are properly formatted
Release 0.3.8
Fix reference to $APP
Please increase the server_names_hash_bucket_size

I use Dokku in a private environment with very long hostname.... 64 was always a lot to short.
create build env for both dokku and new style buildpacks
link to commit id and line in comment
build-env todos
Allow sourcing in any file in .dokkurc

This allows us to configure dokku env-vars individually. Such a feature is useful if a developer would like to enable or disable DOKKU_TRACE without parsing a dokkurc file.
Add a `dokku trace` command to allow easy toggling of the DOKKU_TRACE option
Add a note about enabling `dokku trace` via the cli
Link to gist.github.com
Add documentation for the recent build-env feature addition
Remove user-env-compile plugins from docs
Release 0.3.9