Added ReadPreference to findOne, find, count, and SalatMongoCursor
Updates to scaladoc for updated methods.
Added a spec to test methods with ReadPreference.
Added a spec to test setting of ReadPreference on cursor.
Merge branch 'dao-readprefs' of git://github.com/fdeantoni/salat into fdeantoni-dao-readprefs

Conflicts:
	salat-core/src/main/scala/com/novus/salat/dao/SalatMongoCursor.scala
Fix failing JsonSpec by using appropriate BigInt serialization strategy to meet test expectations.
Scalariform