fix skipping async validator will always fail if condition is un-fulfilled

If the validator configured with `{async:true}` option and `if/unless`
condition, validator should be skipped when the condition is un-fulfilled,
so the validator should be pass.

But currently, when skipping the validator, it calls `done(true)` which
accepts a `fail` flag as a param, this will fail the entire validation.

Signed-off-by: Clark Wang <clark.wangs@gmail.com>
fix embedsOne error when embed instance is undefined or null

Signed-off-by: Clark Wang <clark.wangs@gmail.com>
docs.json: add lib/model.js
Fix a typo
Allow more flavors of nullable values from DB discovery
Merge pull request #354 from clarkorz/fix/skip-validation

fix skipping async validator will always fail if condition is un-fulfilled
Merge pull request #360 from clarkorz/fix/embedsOne-errors

fix embedsOne error when embed instance is undefined or null
Merge pull request #364 from strongloop/feature/include-base-model-in-apidocs

docs.json: add lib/model.js
Relax the id comparison
v2.12.0
Merge branch 'release/2.12.0' into production
Merge tag 'v2.12.0'

2.12.0

 * Relax the id comparison (Raymond Feng)

 * Allow more flavors of nullable values from DB discovery (Raymond Feng)

 * Fix a typo (Raymond Feng)

 * docs.json: add lib/model.js (Miroslav Bajtoš)

 * Update README.md (Rand McKinney)

 * fix embedsOne error when embed instance is undefined or null (Clark Wang)

 * Be explicit: set RelationDefinition multiple flag (Fabien Franzen)

 * Allow hasOne relation to have a scope option (Clark Wang)

 * fix skipping async validator will always fail if condition is un-fulfilled (Clark Wang)
Fixed the haversine formula to calculate distance between 2 points properly
renamed intermediary variable
Added mocha tests for GeoPoint
Fixed indentation
Fixed constructor parameters and added bdd tests for constructor validation
Additional formatting
Added test for toString()
fix default include in default scope fails findById

Signed-off-by: Clark Wang <clark.wangs@gmail.com>