Ember Data doc updates
Add ember data core concepts
Add architecture overview for ember data
Store and finding records docs
Add application template cross-reference
Guide <ul>s should use a disc
Tons more ember data docs
Wordsmithing
Update defining-models.md with typo

changed "bed" to "best" under Explicit Inverses
Update defining-models.md be consistent with capitalization of Attr types

SHould these be titlecased or lower case?
`string`, `number`, `boolean`, and `date`.

Here they are Capitalized but in 
CREATING CUSTOM TRANSFORMATIONS
section they are lower case.
Better explain pushing vs. requesting
WIP on pushing records
Updated routing `model` guide
Expand routing guide on model hook
Get ember data beta guides ready