Fix 'recpies' typo
Accurately document unicorn_env, app_env, and unicorn_config_filename variables

This is the first step towards resolving #46 and #64.
Make unicorn_env default to rails_env or 'production'

This contributes towards resolving #46 and #64.
Rename `app_env` to `unicorn_rack_env` and fix default value

This is the final commit in the series which fixes #46.
Add unicorn_options variable which allows passing of arbitrary options to unicorn

Fixes #64 via:

    set :unicorn_options, '-N'

(although I'm not sure why you'd need this over setting :unicorn_rack_env to 'none').
Add unicorn:show_vars task for debugging variable values
Eliminate unnecessary blanket rescue
Clarify the default for unicorn_user
Embed multistage docs directly within the README

Accurate docs for this is now coupled to the release, and should not
live in the wiki, since claims about app_env in older versions may or
may not be accurate, but they certainly aren't at this point in the
code base.
ensure RAILS_ENV is set correctly
simplify quoting of long shell command
add some quotes to be safe
add NEWS.md to aid with upgrades
fix incorrect docs for app_subdir
remove unnecessary use of fetch
move primary and secondary config paths into _cset section

Grouping all path calculations together improves legibility and maintainability.
rename primary_config_path and secondary_config_path for clarity
add relative path calculations in preparation for pid auto-detection

Also re-order and re-structure assignment and display of variables
for legibility.
attempt to auto-detect path of pid file (fixes #7)
fix tense used when describing default variable values