Massive refactoring of build.py to merge DesignMatrixBuilder into DesignInfo

Notable changes:
- DesignInfo now exposes lots more metadata about how exactly different
  factors and terms are coded.
- In fact, it exposes enough more metadata that you can now reconstruct
  a design matrix entirely from a DesignInfo, so DesignMatrixBuilder
  becomes redundant and is removed in favor of DesignInfo.
- DesignInfo's constructor is very different; in particular, removed the
  option of specifying terms as strings, which was only useful for
  interoperability with competing formula libraries. Four years later, no
  such competitors have appeared, so I can't be bothered to keep maintaining
  this. Will re-add later if someone actually wants to use it.

This versions works and passes tests, but a bunch more tests need to be
added.

This fixes #61, and sets us up to implemented pickling support (#26, #67).

Author: njsmith

doc/API-reference.rst

@@ -105,11 +105,35 @@ Design metadata
 
          di.term_slices
 
+   .. attribute:: factor_infos
+
+      A dict mapping factor objects to :class:`FactorInfo` objects
+      providing information about each factor. Like :attr:`terms`,
+      this may be None.
+
+      .. ipython:: python
+
+         di.term_slices
+
+   .. attribute:: term_codings
+
+      An :class:`~collections.OrderedDict` mapping each :class:`Term`
+      object to a list of :class:`SubtermInfo` objects which together
+      describe how this term is encoded in the final design
+      matrix. Like :attr:`terms`, this may be None.
+
+      .. ipython:: python
+
+         di.term_codings
+
    .. attribute:: builder
 
-      A :class:`DesignMatrixBuilder` object that can be used to
-      generate more design matrices of this type (e.g. for
-      prediction). May be None.
+      In versions of patsy before 0.4.0, this returned a
+      ``DesignMatrixBuilder`` object which could be passed to
+      :func:`build_design_matrices`. Starting in 0.4.0,
+      :func:`build_design_matrices` now accepts :class:`DesignInfo`
+      objects directly, and writing ``f(design_info.builder)`` is now a
+      deprecated alias for simply writing ``f(design_info)``.
 
    A number of convenience methods are also provided that take
    advantage of the above metadata:
@@ -120,8 +144,14 @@ Design metadata
 
    .. automethod:: slice
 
+   .. automethod:: subset
+
    .. automethod:: from_array
 
+.. autoclass:: FactorInfo
+
+.. autoclass:: SubtermInfo
+
 .. autoclass:: DesignMatrix
 
    .. automethod:: __new__

doc/conf.py

@@ -2,7 +2,7 @@
 
 # General information about the project.
 project = u'patsy'
-copyright = u'2011-2013, Nathaniel J. Smith'
+copyright = u'2011-2015, Nathaniel J. Smith'
 
 import sys
 print "python exec:", sys.executable