Update tests to use FactCheck
Implement `Base.get` for BSON objects

This commit also changes the behavior of `get` to be more consistent with the rest of Julia. If a key is not found, the default is to throw an error, unless a default is explicitly provided.
Implement `Base.getindex(::BSONObject, ...)`
Wrap `mongo_cmd_drop_db` as `dropdb!`
Add tests for basic mongo operations
Loosen types to allow for BSONObjects or Dicts (closes #16)
Align constant declarations
Dispatch on value type in BSON's `append`

This allows the compiler to specialize the code for each value type and is generally preferred to switching with an explicit `typeof`.
Update tests for new version of FactCheck
Namespace BSON module as Mongo.BSON; rename run.jl => test.jl
Update README to use Dicts instead of BSONObjects
Require julia 0.2-
Update mongo-c function calls that changed in 0.8 of libmongoc