Initial implementation for function expressions
Documenting new id() function
Documenting FunctionExpression
Adding some doc blocks to FunctionExpressionTest
Starting a trait for constucting common SQL functions
Adding support for passing a closure to select(), it should return the
list of fields to be selected
Adding file I missed in previous commit
Starting some code on using FunctionsTrait
Bringing code up to date with recent renamings
Simplifying parameter binding by making it all the same, this also
resolves a potential issue that was made evident on cyclic references
not being able to be traversed