dir adapter uses schema if provided
fixed bug when there is no header
dir_adapter ignores files that starth with '.'
raise the real NotImplementedError
Views and Schema evaluation is now preformed by 
the query object prior to compilation.

Each RelationalOp from the AST now has a schema
attribute which is None after parsing. The
query on instantiation walks the tree and
set's the appropriate schema on each node.
Functions that compile expressions now only need
to work with a schema.
Separate rewriting the tree for aggregation pushing
from compiling the projection op.

Just keeping things tidy.
No longer return Relation objects as the result of
a compilation step, now a simple iterator will do.
Moved NullAdapter to it's own module under
splicer.adapters.

Also removed NullRelation as it's no longer needed.
resolve_shema() now performs the walk, fixed ops
that override new to properly set the schema
experiment with allowing adapter.schemas to return expressions
resolve functions
implemented not equals on ast nodes
use Query object to interpret schemas
method for comparing two query trees during tests
relation functions resolve to relations, still playnig with this
- Fixed dir adapter tests to expect more arguments

- dir_adapter takes a schema
Make LoadOps and Relations comparable to each other if their name matches.

Mostly useful for testing.
fixed typos
Keep interpreting tree until we reach real relations