DATAMONGO-758 - Current mongodb Versions only support to explicitly exclude the _id property in a projection.

Added guard to FieldProjection.from within ProjectionOption to prevent users from excluding fields other than "_id".
DATAMONGO-757 - Align output of projection operation with MongoDB defaults.

Adjusted FieldProjection to generate an appropriate representation of included / excluded fields (namely :1 for included and :0 for excluded).
Polished guards to handle only _id is allowed to be excluded (DATAMONGO-758).

Original pull request: #76.