Check to make sure libcasacorewrapper.so is built
Rename table finalizer to close and export close
Delete unused function
Refactor and reorganize tables.jl

The most substantial change here is to make addColumn take a type
instead of a string. This accompanies a refactor that makes the C code
use C++ templates.
Define putAntenna1 and putAntenna2
Don't export close

I need to look a little bit more closely at how to "close" Tables. At
the moment, if you actually call close on the table, you get a segfault
when Julia later tries to finalize the object.
Assorted interface and documentation fixes
Merge pull request #12 from mweastwood/improvements

Make the MeasurementSet interface more consistent