Implement better support for embedded/anonymous types

[mkeeler]

Right now you have to use the <embedded struct type name>.<field name> to select an field in an embedded type. In Go we can elide the type name and just select the field name so go-bexpr should allow similar things.

[danishprakash]

@mkeeler I don't see any labels (and sorry for the noise on other issues too) but would this be a good issue for a newcomer to the project to work on? thanks