Support for overriding MongoClientOptions in casbah driver

[dpfeiffer]

Hi,

this PR solves #131. Actually doesn't allow to override settings specified in the URI because in the Java MongoDB Driver settings from the URI override those within the MongoClientOptions.

I decided to exclude some of the values from MongoClientOptions because they could be dangerous as discussed in #23 (readPreference, readConcern).

[natewarr]

👍 Nice timing. Was looking for this exact functionality.

[scullxbones]

First - thanks for the contribution! This looks pretty good to me. Thanks for the docs and the spec.

Two things:

• the options that refer to time (ms) - can they be changed from ints to typesafe config durations? It would make them easier to use.
• the spec could use a test that verifies that given an overridden config, the values change. Just a couple fields is fine, don't need to change all of them.

Question - are the values used in the reference.conf the defaults for the builder?

[dpfeiffer]

Hi,

• sure, the naming is copied from (or follows) the naming convention of the URI config parameters. I propose to just remove just the ms but keep the names near to the URI parameter names.
• will add that one
• the values in the reference config are the ones from the builder, I first thought of using the builder as fallback, but for the RxClientSettings the values are also in the reference.conf so I decided to do it the same way

[scullxbones]

Looks good, thanks!