support engine options overrides by output type

- allow engine options to be overridden for specific output types
- move default options under 'default' key
- set default options for haml and slim
- merge data from default site yaml when loading site yaml
additional sane defaults
fix how Slim is loaded
Relative extension: errors should be reported in console
Log properly for Extension Relative
fix typos in help, add missing ninesixty import
use DateTime instead of Time to preserve tz info
Merge 6dca05cdd2f233410c971050529ebd356e59f8ff into c5c0cc2df3d7a9f3f38c80cef086e36ac3274dee
Merge pull request #242 from ge0ffrey/patch-1

Relative extension: errors should be reported in console
Merge pull request #240 from mojavelinux/per-output-engine-config

support engine options overrides by output type
Merge commit 'refs/pull/244/merge' of github.com:awestruct/awestruct

Conflicts:
	lib/awestruct/extensions/posts.rb
Fixes issue #241
Merge pull request #245 from LightGuard/issue_241

Fixes issue #241
disable test for --run until implemented
switch test to pending
Merge pull request #243 from mojavelinux/help-typo

fix typos in help, add missing ninesixty import
more detailed exception message when rendering fails
Merge 7f6931d55028b9bfdfd1fe2d4b729883bc253912 into 7c8b4e70ac70d981cc456c4965ffe63dce5f0deb
Joining backtrace array using newline
change engine opts to a flat config structure

- include a new theory for matching the engine format option
- test files w/ atom extension